Magnetic recording and reproducing apparatus for controlling the tension of a magnetic tape

ABSTRACT

A magnetic recording and reproducing apparatus for recording a desired sound or picture signal to a magnetic tape by a magnetic head. At the time of normal-speed recording and reproduction, the magnetic tape is taken up at a constant speed, but by changing the tape travelling speed of the tape on the rotary drum, DTF control and high-speed noiseless reproduction are enabled. The tension of the tape on the entrance side of the rotary drum is controlled to a desired value. This apparatus includes a tape tension actuator and a tape drawing actuator on the entrance side and on the exit side, respectively, of the rotary drum. In DTF control, both tape actuators correct a tracking error of the tape in cooperation with each other. In high-speed noiseless reproduction, both tape actuators are differentially driven so as to lower the tape travelling speed on the rotary drum. Both tape actuators are driven in feedback control using the modern control.

This application is a continuation of application Ser. No. 08/186,503,filed on Jan. 26, 1994, abandoned, which is a Rule 1.62 continuation ofSer. No.: 07/624,418 filed Dec. 6, 1990, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic recording and reproducingapparatus and, more particularly, to a high-speed reproducing system, atracking control system and a tension control system for a video taperecorder (hereinunder referred to as "VTR") of a helical scanningsystem.

2. Description of the Related Art

In a conventional auto tracking reproducing apparatus in a VTR of ahelical scanning system, a video signal reproducing magnetic head isgenerally mounted on an electromechanical transducing element(hereinunder referred to as "head actuator"). At the time ofreproduction, the head actuator is driven perpendicularly to thedirection of the travel of a recording track, thereby giving automaticfollowing control over the magnetic head so as to prevent the magnetichead from leaving the recording track.

Various methods have been proposed and already put to practical useconcerning a technique of enabling the magnetic head mounted on the headactuator to automatically follow the recording track, which is called anauto tracking control technique.

For example, several kinds (e.g., four kinds) of pilot signals fortracking low frequencies in a band other than a video signal band areoverlapped with a video signal and separate pilot signals are recordedon several adjacent (four) tracks, as known in an 8-mm VTR format. Inthis pilot system, a tracking error signal is detected by a differencein a crosstalk level between the left and right tracks at the time ofreproduction.

In a wobbling system which has been put to practical use in 1-inch VTRproduced by Ampex, D-2 format digital VTR DVR-10 produced by SonyCorporation and the like, the magnetic head is forcibly vibratedminutely in the direction of the track width at a constant frequencywhich is called a wobbling frequency. The reproduction envelope signalfrom the magnetic head is synchronously detected at the wobblingfrequency, whereby a tracking error signal is detected.

In a mountaineering system, which has been put to practical use in VHSVTR, NV-10000 produced by Matsushita Electric Industrial Co., Ltd., VHSVTR F75 produced by Mitsubishi Electric Copr. and the like, thereproduction envelope signal from the magnetic head is supplied to asample-and-hold circuit at the central portion of the field which hasbeen read. The voltage to be applied to the actuator or the rotationphase of the capstan motor is then changed by one step (e.g., increased)and the envelope level of the next frame is compared with the value ofthe sample and hold value. This series of operation is repeated untilthe envelope level of the next frame becomes smaller. When the envelopelevel of the next frame becomes smaller, the direction of the appliedvoltage is reversed and the envelope level of the reproduction signal isupwardly converged toward the maximum value.

In a conventional auto tracking reproducing apparatus, a tracking erroris detected by the above-described various tracking error detectingmethods and the detected tracking error is fed back by the head actuatorwhich is accommodated in the rotary drum.

Such a movable head is not only used for dynamic track following(hereinunder referred to as "DTF") control for correcting a trackingerror during normal-speed reproduction but also often used at the timeof superior reproduction (high-speed reproduction, slow reproduction andstill reproduction).

As an example of such a movable head used for noiseless superiorreproduction, the system of a movable head described on p. 41 ofNational Technical Report. Vol. 28, No. 3, June (1982) is schematicallyshown in FIG. 75.

In order to briefly explain the high-speed superior reproducing methodusing this known system FIG. 76 shows the high-speed superiorreproduction servo system. In FIG. 76, a rotary magnetic head 1 isdriven by a head actuator 2 perpendicularly to the direction of thetravel of the tape. From the reproduction envelope signal of themagnetic head 1, an amount of tracking error is detected by a trackingerror detector 3 and a tracking error signal is output. An inclinationcorrection pattern generator 4 corrects the inclination of the magnetichead 1 from the tape speed information so that the angle at which themagnetic head 1 scans a tape (not shown) agrees with the angle of therecording track (not shown) and generates a track trace pattern for themagnetic head 1. The tracking error signal from the tracking errordetector 3 and the inclination correction pattern from the inclinationcorrection pattern generator 4 are added by an adder 5.

The operation of a conventional system will now be explained. The angleat which the magnetic head 1 traces the tape at the time of normal-speedreproduction (hereinunder referred to as "speed 1") is the same as theangle of the recording track. However, at the time of reproduction at adifferent speed, since the angle at which the magnetic head 1 traces thetape does not agree with the angle of the recording track, off-track(hereinunder referred to as "inclination error") is produced and a noiseis produced on a reproduced picture.

As an example, FIGS. 77 and 78 schematically show the relationshipbetween the recording track pattern on the tape and the trajectories ofthe magnetic head 1 produced at the time of reproduction at a speed fivetimes as high as the normal speed (hereinunder referred to as "speed 5")in the forward direction and the reverse direction, respectively. InFIGS. 77 and 78, the symbol A represents a trajectory of the magnetichead 1 produced at the time of normal-speed reproduction, B a trajectoryof the magnetic head 1 produced at the time of reproduction at speed 5,and C a trajectory of the magnetic head 1 produced at the time ofreproduction at speed 5 in the reverse direction. As is obvious fromFIGS. 77 and 78, the trajectory of the magnetic head 1 must be correctedto be A from B or C for the purpose of noiseless reproduction.

FIG. 79 schematically shows an inclination error pattern of the magnetichead 1 produced at the time of reproduction at a speed n times as highas the normal speed (hereinunder referred to as "speed n", n is anygiven real number).

It is now assumed that a VTR has a guard bandless recording systemutilizing an azimuth loss. If it is assumed that T is a 1/2 period ofthe rotary drum and t_(p) is a track pitch, the inclination error whichmay be caused at the time of reproduction at speed n is represented byt_(p) (n-1), wherein n is an integer. In this way, the inclination errorpattern is represented by a function having n as a parameter. In otherwords, the inclination error pattern changes depending upon the tapetravelling speed. The inclination correction pattern generator shown inFIG. 76 is so designed as to generate an inclination correction patternby utilizing tape speed information such as a capstan FG signal.

When the inclination correction pattern is supplied to the head actuator2, the inclination of the magnetic head 1 is corrected so as to move inparallel to the trajectory of the recording track even at the time ofreproduction at a different speed. However, the mere displacement of themagnetic head 1 in conformity with the angle of the recording trackfurther generates off-track due to the linearity of the trajectories ofthe recording track and the magnetic head 1 or the phase deviation ofthe track. In order to prevent such off-track, an auto tracking controlsystem by a closed loop, which is represented by the surrounding brokenline in FIG. 75, is generally added.

Any system such as the pilot system, wobbling system and mountaineeringsystem described above may be adopted as the controlling method for theauto tracking control system, but in order to obtain a high-definitionimage even at the time of production at a different speed, since it isnecessary that the magnetic head 1 follows the nonlinearity of therecording track (hereinunder referred to as "track rolling"), it isdesirable to adopt the pilot system or the wobbling system which allowsa comparatively wide controlled region. Since the controlling method andoperation of the auto tracking control system have already been known, adetailed explanation thereof will be omitted here.

The tape tension control will now be explained.

FIG. 80 shows the structure of a magnetic tape travelling system of avideo tape recorder of a VHS system as a magnetic recording andreproducing apparatus which is described on p. 187 of Introduction toMagnetic Recording Technique, by Yokoyama, edited by Sogo DenshiShuppan-sha. In FIG. 80, a video tape (magnetic tape) is supplied from afeed reel 6 and the tension of the magnetic tape travelling system isdetected by a back tension post 7. The information recorded on the videotape is temporarily erased by an all-width erase head 8. The magnetictape travelling system is stabilized by impedance rollers 9 and 10. Arotary drum 11 includes an upper cylinder 12 and a lower cylinder 13. Avideo head 14 is secured to the upper cylinder 12. The sound signal onthe linear track of the video tape is erased by a sound erase head 15,and thereafter a sound and a control pulse are recorded on the lineartrack by a sound control head 16. A pinch roller 18 is provided so as toclamp a capstan shaft 17 and a video tape at a constant pressing force.The capstan shaft 17 is opposed to the pinch roller 18 so as to controlthe deviation of the trajectory of the video head 14 from the videotrack on the video tape by causing the video tape to travel. A take-upreel 19 is provided for taking up the video tape.

FIG. 81 shows the structure of a conventional tension control mechanism(tension servo mechanism). In FIG. 81, the rotation of the feed reel 6is suppressed by a hub brake 20. The tension of the magnetic tapetravelling system is detected by a tension control arm 21. The forceproportional to the amount of displacement of the tension control arm 21is applied to the hub brake 20 by a spring 22, the spring 22 beingcapable of varying the force which is applied to the tension control arm21. A tension adjust lever 23 for adjusting the reference tension of thetension control mechanism is connected to the spring 22.

The operation of the conventional tension control mechanism will now beexplained.

The video tape supplied from the feed reel 6 is clamped between thepinch roller 18 and the capstan shaft 17 and stretched by the rotationof the capstan shaft 17. Thereafter, the video tape is wound around thetake-up reel 19. During this time, it is necessary that the tension ofthe magnetic tape travelling system is controlled to a constant value sothat the spaces between the video tape and the all-width erase head 8,the video head 14, the sound erase head 15, the sound control head 16and the like are optimum. Needless to say, when the tension of thetravelling system is increased, the spaces between the heads and thetape are reduced, so that the high-frequency characteristics of therecording and reproducing system are enhanced but the scuffs of the tapeare increased and the durability of the apparatus in the still state forcontinuously reproducing the same track is deteriorated. In addition,the wear of the heads are increased. On the other hand, if the tensionof the travelling system is reduced, since the spaces between the headsand the tape are increased, the high-frequency characteristics of therecording and reproducing system are deteriorated. As a countermeasure,a conventional VTR is provided with a tension control mechanism such asthat shown in FIG. 81. In FIG. 81, for example, if the tension of themagnetic tape travelling system is increased, since the balance betweenthe tension control arm 21 and the spring 22 is disturbed, the spring 22is extended. At this time, the hub brake 20 is relaxed and the rotationof the feed reel 6 is made free, whereby the amount of feed of videotape is increased. As a result, the tension of the magnetic tapetravelling system is restored to the original tension. In this way, thetension of the magnetic tape travelling system is kept constant.

In a high-definition TV or a digital VTR for digitally recording andreproducing a video signal and a sound signal, since the amount ofinformation recorded is greatly increased, the technique of high-densityrecording and reproduction with high-accuracy DTF control are essentialin order to enable long-time recording on a cassette tape of a limitedsize.

In a DTF apparatus in a conventional VTR, since the means for trackingerror correction is merely a movable head accommodated in the drum, theDTF control capacity is determined by the performance of the headactuator for moving the movable head.

As the head actuator 2 which is generally used for DTF control in a widefrequency band with a high accuracy, one which has no phase shift up toa comparatively high frequency, for example, up to the vicinity of 1 KHzto several KHz is selected by virtue of its good control capacity. Thehead actuator 2 which does not cause a phase shift up to a highfrequency is required to have a mechanical characteristic which does notresonate up to a high frequency. The primary mechanical resonancefrequency of a general actuator is obtained by dividing the root of thequotient obtained by dividing the spring constant of the actuator by themass of the movable portion of the actuator by 2 π. A high primaryresonance frequency is therefore obtained either by lightening the massof the movable portion of the actuator or by increasing the springconstant of the actuator.

As described above, a movable head is generally not only used for DTFcontrol at the time of normal-speed reproduction but is also often usedat the time of superior reproduction. In a high-speed noiselessreproducing apparatus in a conventional VTR, the tracking error iscorrected by moving the magnetic head in the direction of the width ofthe recording track by the head actuator. The amount of tracking errorwhich is correctable is therefore limited to the range in which the headactuator is movable. For this reason, the range in which the headactuator for driving the magnetic head is movable is preferably as wideas possible. In a conventional structure, however, the head actuatormust be accommodated in the rotary drum, the outer diameter of which isdetermined by the standard, so that a small-sized head actuator isnaturally required.

To meet such demand, a piezoelectric element consisting of two pastedpiezoelectric sheets (hereinunder referred to as "bimorphous cell"), alamination type piezoelectric element with a displacement enlargingmechanism, such as a lever and a buckling spring attached thereto, and amoving coil supported by a spring and electromagnetically driven in amagnetic circuit (hereinunder referred to as "electromagnetic actuator")have been proposed as a small-sized head actuator which has a widemovable range, and some of these have been put to practical use.

The cases of using these head actuators for DTF control and high-speednoiseless reproduction will be considered in the following discussion.

It is first assumed that a bimorphous cell is used as a head actuator. Abimorphous cell is known among piezoelectric elements as an elementwhich has a large amplitude for the driving voltage. The amount ofdisplacement ξ of a bimorphous cell is represented by the followingequation:

    ξ=d.sub.31 ×V×l.sup.2 t.sup.2 ×S.sub.k ×R

wherein ξ: displacement, V: applied voltage, d31: piezoelectricconstant, l: effective length, t: thickness of one sheet ofpiezoelectric element, S_(k) : electrode coefficient (0.94 to 0.95), R:loss factor (0.9)

The piezoelectric constant d31 is a function of the applied voltage V,and when the applied voltage V is large, d₃₁ also becomes large. S_(k)and R are constants determined by the configuration of the bimorphouscell.

Thus, it is understood that the amount of displacement ξ of thebimorphous cell is determined by various factors.

In order to increase the primary mechanical resonance frequency of abimorphous cell for DTF control, it is necessary to increase thethickness t of one sheet of piezoelectric and reduce the effectivelength l. In other words, it is necessary to reduce l/t. However, if l/tis reduced, the amount of displacement ξ of the bimorphous cell is alsoreduced by the square of l/t, which is disadvantageous to the bimorphouscell for high-speed superior reproduction which requires a largeamplitude. That is, a bimorphous cell for DTF control and a bimorphouscell for high speed superior reproduction have antipodal requirements.In most cases, the system of a bimorphous cell is therefore composedwith more importance attached to either DTF control or high-speedsuperior reproduction.

For example, in a tape format having a wide track pitch such as thetapes of a publicly used VTR of VHS system and β system and an 8-mmtape, since DTF control with a comparative accuracy is not required, thehead actuator is mainly used for high-speed superior reproduction, as inknown systems.

In this case, a head actuator having a large piezoelectric constant d₃₁is selected so as to have a large amplitude and a small mechanicalresonance gain. However, it is the effective length l of the bimorphouscell in the term of a square that mainly influences the amount ofdisplacement ξ, and the larger the effective length l, the larger theamount of displacement ξ.

As the head actuator is accommodated in the rotary drum having a limiteddiameter, as described above, the effective length l is also limited.Various attempts have been made at increasing the effective length l asmuch as possible. For example, there are an annular bimorphous cell 2aand carrying heads 14a and 14b shown in FIG. 82, which is disclosed inJapanese Patent Laid-Open No. 22285/1980 and leaf bimorphous cells 2band 2c shown in FIG. 83, which are disclosed in Japanese PatentPublication No. 41130/1988. However, even if the amount of displacementξ is increased by increasing the effective length l in this way, thereremains still another problem.

FIG. 84 shows the relationship between the effective length of abimorphous cell and the inclination of a magnetic head. As is clear fromFIG. 84, a large amplitude increases the inclination of the magnetichead, which inevitably results in the deterioration in the picturequality.

On the other hand, in a tape format having a narrow track pitch such asthe tapes of a high-definition TV VTR and a digital VTR, since DTFcontrol with a high accuracy in a wide frequency band is essential, abimorphous cell having a high primary mechanical resonance frequency isselected even at the sacrifice of the possible speed in high-speedsuperior reproduction.

As described above, it is impossible that a bimorphous cellsimultaneously satisfies both requirements for DTF control in a widefrequency band with a high accuracy and for high-speed superiorreproduction.

Secondly, it is assumed that a lamination type piezoelectric elementwith a displacement enlarging mechanism attached thereto is used as ahead actuator. An example of this type of head actuator is described inNEC Technical Reports, Vol. 40, No. 5. pp. 118 to 122 (1987). In thisexample, no inclination of the head is caused by displacement unlike abimorphous cell, but since a lamination type piezoelectric elementhaving a small amount of displacement is used as a driving element, itis impossible to obtain a large amount of displacement. Even if theamount of displacement is largely increased by a level or a bucklingspring, when the head actuator is accommodated in the rotary drum of theVTR, the displacement is influenced by the centrifugal force of thedisplacement enlarging mechanism, thereby causing an offset in thedisplacement.

Thirdly, it is assumed that an electromagnetic actuator is used as ahead actuator. An example of the electromagnetic actuator is disclosedin Japanese Patent Laid-Open No. 173219/1988. An electromagneticactuator is known to have a comparatively large amount of displacementin comparison with the above-described two actuators. The structure ofan electromagnetic actuator is shown in FIG. 85.

In FIG. 85, the head 14 is held by a movable coil 24 and the movablecoil 24 is supported around a permanent magnet 25 in such a manner as tobe movable in the axial direction. The position of the head 14 istherefore adjustable as desired by supplying an appropriate drivingcurrent to the movable coil 24.

Such an electromagnetic actuator has many advantages when it is used forhigh-speed superior reproduction. For example, a driving voltage V ofseveral volts is sufficient, and there is no hysteresis or noinclination of the head. The high reliability is secured. There is nodeterioration with time. In addition, since an electromagnetic actuatoris cheap, it is suitable to practical use for a publicly used VTR.However, a general electromagnetic actuator for superior reproductionhas a frequency response characteristic such as shown in FIG. 86. Whenan electromagnetic actuator is used for superior reproduction, since thespring constant is set at a weak value with respect to the forcegenerated by the coil in order to increase the amount of displacement,the mechanical resonance frequency is low. In addition, it is necessaryto sufficiently separate the driving coil from the magnetic head througha certain member in order to avoid the influence of the magnetic fieldgenerated from the driving coil while driving the actuator. Since thesecondary resonance frequency caused by this member exists comparativelyclose to the first resonance frequency, the DTF control system must becomposed by a compensation outside the resonance for controlling in alow frequency band than the primary resonance frequency. That is, sinceit is impossible to enlarge the controlled region, a DTF control in awide frequency band with a high accuracy is not realized.

If the spring constant is increased for DTF control, DTF control in awide frequency band with a high accuracy is possible. However, in orderto use such an actuator for superior reproduction, it is necessary toincrease the force generated by the driving coil for the purpose ofobtaining a displacement with a large amplitude. It is thereforenecessary to apply a large current, which is a problem in the respect ofheat generation or the like.

Consequently, it is also difficult that an electromagnetic actuator hasa DTF control capacity and a high-speed superior reproducing capacity atthe same time.

To sum up the above explanation, it is impossible in a conventionalapparatus to simultaneously realize DTF control in a wide controlledregion such as several hundred Hz with a high accuracy and noiselessreproduction at a high speed such as several ten times as high as thenormal speed.

The problems of a tension control device in a conventional magneticrecording and reproducing apparatus will now be explained.

FIGS. 87 and 88 show a conventional magnetic recording and reproducingapparatus, and in particular, a tape tension control device described inJapanese Patent Laid-Open No. 56036/1990. FIG. 87 shows a recording andreproducing state, and FIG. 88 shows a high-speed tape travelling state.

A magnetic tape is drawn out of a tape cassette (not shown) andconstitutes a tape travel path such as that shown in FIG. 87. A tensionlever 28, and arms 29 and 30 are integrally rotatable around a hingedsupport 31.

At the time of recording and reproduction, a tension post 33 is broughtinto contact with the magnetic tape and simultaneously a tension band 34is brought into contact with a feed reel 35 by a slider 32, as shown inFIG. 87. The magnetic tape is fed toward a take-up reel 36 by a capstanat a constant speed and supplied from the feed reel 35. At this time,the moment of the tension lever 28 produced by a spring 38 between atension release lever 37 and the tension lever 28 is balanced with theresultant force of the moment of the tension lever 28 produced by theforce applied to the tension post 33 by the tension between tape guides39 and 40 and the moment produced by the frictional force between thetension band 34 and the feed reel 35. The tension of the magnetic tapeis mainly controlled by the frictional force applied to the feel reel 35by the tension band 34.

For example, if the tape tension becomes larger than the balanced valuedue to an external disturbance, the tape tension between the tape guide39 on the feeding side and the tape guide 40 on the take-up side as seenfrom the tension post 33 also becomes large. As a result, the tensionpost 33 is pushed out to the left-hand side of the balanced positionshown in FIG. 87. The tension lever 28 is thereby rotatedcounterclockwise around the hinged support 31 and simultaneously the arm30 is also rotated counter-clockwise. With the reduction in the contactforce between the tension band 34 and the feed reel 35, the frictionalforce is reduced, and consequently the tension is relaxed, whereby thetension post 33 is restored to the balanced position in the end.

On the other hand, when the tape tension becomes smaller than thebalanced value due to an external disturbance, the frictional forcebetween the tension band 33 and the feed reel 35 becomes large and, as aresult, the tension is increased, whereby the tension post 33 isrestored to the balanced position.

The tape tension is kept constant in this way at the time of recordingand reproduction.

During high-speed tape travel, the tension post 33 is moved to aposition at which the tension post 33 is out of contact with themagnetic tape by the slider 32. The tension band 32 is relaxed to aposition at which the tension band 33 is out of contact with the feedreel 35, so that the tension control mechanism is separated from thetape travelling system. The tension control mechanism is also separatedfrom a capstan 41 and a pinch roller 42. In the case of high-speed tapetravel from the feed reel 35 to the take-up reel 36, the take-up reel 36is rotated at a desired speed to wind the magnetic tape therearound, anda constant load is applied to the feed reel 35 to an extent whichprevents the relaxation of the magnetic tape. On the other hand, in thecase of high-speed tape travel from the take-up reel 36 to the feed reel35, the feed reel 35 is rotated at a desired speed to wind the magnetictape therearound, and a constant load is applied to the take-up reel 35to an extent which prevents the relaxation of the magnetic tape.

In the tape tension control mechanism of a conventional magneticrecording and reproducing apparatus having the above-describedstructure, a special tape tension control other than the application ofa load in the direction contrary to the direction of the travel of thetape is not exerted during high-speed tape travel. Therefore, theconventional tape tension control mechanism cannot respond to atransient tension change, and the tape is sometimes damaged, or by achange in the contacting state between the magnetic head and the tapecaused by a tension change, a fluctuation in the output which leads todeterioration in information is apt to be caused.

In addition, the tension controlled region for the conventional tensioncontrol device is narrow, and a tension change which can be suppressedby the conventional tension control device is only not more than severalHz. Therefore, in a VTR for high-density recording and reproduction suchas a digital VTR adopting this tape tension control device, it isimpossible to constantly keep the optimum space between the magnetichead and the magnetic tape, thereby making good recording andreproduction impossible.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to eliminate theabove-described problems in the known system and to provide a magneticrecording and reproducing apparatus which is capable of realizing bothDTF control in as wide a controlled region as several hundred Hz with ahigh accuracy and noiseless reproduction at a high speed such as severalten times of the normal speed without deterioration in picture quality.

It is another object of the present invention to provide a magneticrecording and reproducing apparatus which is capable of realizing theconstantly optimum contact between the head and the tape by a tensioncontrol in a wide frequency band with a high accuracy, for therebyenabling good recording and reproduction.

To achieve these objects, a magnetic recording and reproducing apparatusaccording to the present invention is provided with a tape drawingactuator and a tape tension actuator on the magnetic tape exit side andthe magnetic tape entrance side, respectively, of a rotary drum with amagnetic head provided thereon in a magnetic tape travel path inaddition to a conventional head actuator.

These tape actuators are operated differentially and are capable offreely changing the tape travelling speed on the head surface.

Use of such tape actuators enables not only DTF control and tensioncontrol separately from each other but also track control and tensioncontrol in a high-frequency band with a high accuracy in combinationwith DTF control and tension control.

Each of the tape actuators is preferably composed of a tape drawing orpushing roller, an arm for rotatably holding the roller with respect toa predetermined rotary shaft, an arm driving portion for driving the armand a position sensor for detecting the displaced position of the armdriving portion. Electrical and mechanical characteristics of both tapeactuators are preferably set to be equal in order to allow them thedifferential action.

In the present invention, the head actuator and the tape drawingactuator are connected in a common DTF control system and constitute acontrol loop for eliminating a tracking error in cooperation by with thenegative feedback of a tracking error signal of the movable head to bothactuators.

The head actuator compensates for a small amplitude in a high-frequencyband of a tracking error, while the tape drawing actuator compensatesfor a large amplitude in a low-frequency band of a tracking error.

In order to combine DTF control with tension control, the controlvoltage generated from the tracking control loop of the tape drawingactuator is supplied to the tape tension actuator, and by thedifferential action of both tape actuators, a desired stable tapetension is obtained, for thereby realizing a good contact between thetape and the head.

In order to properly control the tape tension actuator, it is preferablethat the dynamic characteristic of the tape tension actuator iselectrically estimated and a tension estimating device for electricallysimulating the relationship between the voltage to be input to the tapetension actuator and the displacement of the tape tension actuator isprovided. This relationship is expressed by (inputvoltage)/(displacement) transfer characteristic and the external tensiondisturbance applied to the tape tension actuator can be estimatedtherefrom.

Therefore, if the high-frequency component of the tension error signalis negatively fed back to the tape tension actuator and thelow-frequency component of the tension error signal is negatively fedback to the feed reel motor so that the estimated tension agrees with apreset reference tension, tension control in a wide frequency band isenabled.

In this way, according to the present invention, tracking control in awide frequency band and a wide dynamic range with a high accuracy isenabled in the normal reproduction mode in cooperation with the headactuator having a large high-frequency band gain and the tape actuatorshaving a large low-frequency band gain. By this division of thefrequency band, tracking control in a wide frequency band is realizedeven in a tape format having a narrow track pitch.

According to the present invention, the tape actuators change the tapetravelling speed by the differential action of the tape drawing actuatorand the tape tension actuator, and the change in tension is suppressedby both tape actuators.

The change in tension caused by the electrical or mechanicalcharacteristics of the actuator itself or an external disturbance whenthe pair of tape actuators reciprocate is suppressed by feed backing thesignal generated from the tension estimating device to the tape tensionactuator and the feed reel motor.

By such simultaneous control of DTF and tension, a tracking error iseliminated and a good contact between the tape and the head is obtained,for thereby enabling high-quality signal reproduction duringnormal-speed reproduction.

In the high-speed reproduction mode, the tape is subjected to a rockingmotion by both tape actuators between the entrance and the exit of therotary drum while causing the tape to travel at a high speed, and in thestate in which the tape speed is relatively lowered with respect to thehead, a signal is intermittently reproduced.

In this way, it is possible to intermittently obtain a high-qualityreproduced image even in a high-speed tape travelling state.

In order to rock the tape actuators, a triangular signal having afrequency synchronous with 1/m (m is a positive integer) of therotational frequency of the rotary drum is applied to the actuators.

It is preferable that the tape tension actuator and the feed reel motorare also subjected to tension control during such noiseless high-speedsuperior reproduction.

The present invention is further characterized in that the tension atthe time of recording and reproduction is controlled to be the optimumvalue by using the tape tension actuator.

In the present invention, tension control by the tape tension actuatoris realized independently of DTF control. For this purpose, the tapetension actuator provides a desired tension for the tape at the tapeentrance side of the rotary drum and the tension control system uses the(input voltage)/(displacement) transfer characteristic. The tensioncontrol system estimates the tension which the tape tension actuatorreceives from the tape travelling system and exerts feedback control ofthe tape tension actuator and the feed reel motor so that the estimatedtension agrees with the reference tension.

As described above, according to the present invention, it is possibleto control the tape tension in a wide frequency band with a highaccuracy and to obtain the optimum tape tension both in recording and inreproduction.

The above and other objects, features and advantages of the presentinvention will become clear from the following description of thepreferred embodiments thereof, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a first embodiment of a magnetic recordingand reproducing apparatus according to the present invention;

FIG. 2 is a perspective view explaining the principle of the presentinvention;

FIGS. 3 and 4 are explanatory views schematically showing a change inthe tape travelling speed caused by the operation of a tape actuator inaccordance with the present invention;

FIG. 5 schematically shows the recording track pattern of a VTR;

FIG. 6 shows the (displacement angle)/(torque) characteristic of a tapeactuator according to the present invention;

FIGS. 7A-7C are time charts showing the operation of each element at thetime of high-speed noiseless reproduction;

FIG. 8 schematically shows the mechanical positional relationshipbetween the fixed tape pass rollers and the rotation axis of the movabletape pass roller and the tape actuator in accordance with the presentinvention;

FIG. 9 shows the relationship between the displacement angle and thelength of the drawn tape in FIG. 8;

FIG. 10 shows the relationship between the displacement angle and theamount of displacement in the direction of the width of the recordingtrack of the tape drawing actuator in the first embodiment;

FIG. 11 is a block diagram of a tracking control system in superiorreproduction in the case in which the ideal mechanical characteristicsare obtained in accordance with the present invention;

FIG. 12 is a block diagram of a servo system in the first embodiment;

FIG. 13 is schematically shows a modification of the tape actuators inaccordance with the present invention;

FIG. 14 is a block diagram of the DTF control system in the firstembodiment;

FIG. 15 is a sectional view of the structure of the head actuator in thefirst embodiment;

FIG. 16 schematically shows a tape actuator in accordance with thepresent invention;

FIGS. 17 and 18 schematically show the magnetic circuit explainingprinciple of driving the tape actuator;

FIGS. 19(a1), (a2) and (a3) are sectional views of an embodiment of thetape actuator in accordance with the present invention;

FIGS. 19(b1), (b2) and (b3) are sectional views;

FIG. 20 shows an example of a position sensor of the tape actuator inthe first embodiment of the present invention;

FIG. 21 shows the frequency characteristic of the tape actuator inaccordance with the present invention;

FIG. 22 is a block diagram showing another example of the DTF controlsystem;

FIG. 23 is a block diagram of a DTF control circuit in the presentinvention which is represented by transfer functions;

FIG. 24 shows the pole-positioning in the DTF control system inaccordance with the present invention;

FIG. 25 shows the open loop characteristic of the DTF control system inaccordance with the present invention;

FIG. 26 is a block diagram of a tension control system in accordancewith the present invention;

FIGS. 27 and 28(a) and (b) show other examples of a position sensor ofthe tape actuator in accordance with the present invention;

FIG. 29 is a block diagram of a tension control circuit in the presentinvention which is represented by transfer functions;

FIG. 30 shows the pole-positioning of a tension estimating observer inaccordance with the present invention;

FIGS. 31 and 32 schematically show the balance of the forces of themovable tape pass roller portion;

FIG. 33 is a frequency characteristic diagram showing the estimatingcapacity of the tension estimating device in accordance with the presentinvention;

FIG. 34 shows the transient behavior of the estimated externaldisturbance;

FIG. 35a and 35b show characteristics of the tension control system inaccordance with the present invention;

FIG. 36 is a block diagram of the structure of a hardware in the tensioncontrol system in accordance with the present invention which iscomposed of a high-speed computer such as a microcomputer;

FIG. 37 is a flowchart of the tension estimating algorithm in accordancewith the present invention;

FIG. 38 is a block diagram for realizing Σ in FIG. 37;

FIG. 39 is a perspective view of another example of the tape actuator inaccordance with the present invention;

FIG. 40 is a block diagram of a second embodiment of the presentinvention;

FIG. 41 is the block diagram shown in FIG. 40 which is represented bytransfer functions;

FIG. 42 shows the external disturbance suppressing characteristic of theexternal disturbance suppressing loop of the tape actuator;

FIG. 43 shows the structure of a tension control mechanism using thetension control system in a third embodiment of the present invention;

FIG. 44 shows the structure of a modification of the tension controlmechanism shown in FIG. 43;

FIG. 45 shows the structure of an optical sensor for detecting theamount of displacement of the tension arm shown in FIG. 43;

FIG. 46 shows the structure of a modification of the optical sensorshown in FIG. 45;

FIG. 47 is an explanatory view of a magnetic sensor for detecting theamount of displacement of the tension arm shown in FIG. 43;

FIG. 48 is an explanatory view of a magnetic sensor for detecting theamount of displacement of the tension arm shown in FIG. 44;

FIG. 49 is a block diagram of the tension control system in the thirdembodiment;

FIG. 50 is a block diagram of the principle of control of the tensioncontrol system shown in FIG. 49 which is represented by transferfunctions;

FIG. 51 is a block diagram of the principle of control of the tensioncontrol system having no driving portion which is represented bytransfer functions;

FIG. 52 is a detailed sectional view of a tape actuator drivingmechanism in the third embodiment of the present invention;

FIG. 53 is a partially cutaway perspective view of the tape actuatormechanism shown in FIG. 52;

FIG. 54 is a plan view of the main part of the movable coil portion andthe permanent magnet showing the positional relationship thereof;

FIG. 55 is a sectional view of the structure of the main part of a lightemitting portion;

FIG. 56 is a schematic plan view of a light receiving element showingthe positional relationship between a ray and the light emittingelement;

FIG. 57 is a sectional view of another example of the tape actuatordriving mechanism;

FIG. 58 is another example of a tape actuator with a reflecting mirrortype position detector mounted thereon;

FIG. 59 is a plan view of the main part of another example of thepermanent magnet shown in FIG. 54;

FIG. 60 is a sectional view of still another example of a tape actuatorprovided with a position sensor having a light shielding plate;

FIGS. 61 and 62 show further examples of a tape actuator provided with aposition sensor having a Hall element;

FIGS. 63 to 65 are plan views of a magnetic recording and reproducingapparatus with the tape actuators in accordance with the presentinvention mounted thereon, wherein

FIG. 63 shows the state of normal-speed recording/reproduction;

and FIGS. 64 and 65 show the state of superior reproduction;

FIG. 66 is a plan view of the main part of another embodiment of amagnetic recording and reproducing apparatus according to the presentinvention after tape loading;

FIG. 67 is a plan view of the main part of a magnetic recording andreproducing apparatus shown in FIG. 66 before tape loading;

FIG. 68 is a detailed side view of a device for regulating the magnetictape in the vertical direction in accordance with the present invention,seen in the direction of the travel of the magnetic tape;

FIG. 69 is a partially sectional view of the details of a mechanism ofvertically moving the tape pass roller on the take-up reel side inaccordance with the present invention;

FIG. 70 is a plan view of the main part of still another embodiment of amagnetic recording and reproducing apparatus according to the presentinvention after tape loading;

FIG. 71 is a plan view of the main part of the magnetic recording andreproducing apparatus shown in FIG. 70 before tape loading;

FIG. 72 is a detailed sectional view of the embodiment shown in FIGS. 70and 71 showing the tape actuator disposed on the under surface of thebase;

FIGS. 73 and 74 show the operation of the tape actuators in theembodiment shown in FIG. 70 and 71 at the time of superior reproduction;

FIG. 75 shows the system of a conventional magnetic reproducingapparatus;

FIG. 76 shows the high-speed superior reproduction servo system in aconventional magnetic reproducing apparatus;

FIGS. 77 and 78 show the relationships between the tape pattern and thetrajectory of the scanning magnetic head in the cases of normal-speedtravel, and reversely travelling at a speed five times as high as thenormal speed, respectively;

FIG. 79 schematically shows inclination error patterns which are to befollowed by the magnetic head in a conventional magnetic reproducingapparatus;

FIG. 80 shows a magnetic tape travelling system in a conventional VTR;

FIG. 81 shows a conventional tension control mechanism;

FIGS. 82 and 83 are plan views of conventional head actuators;

FIG. 84 shows the relationship between the effective length of thebimorphous cell and the inclination of the magnetic head in aconventional head actuator;

FIG. 85 is a sectional view of a conventional head actuator;

FIG. 86 shows the frequency characteristic of the head actuator shown inFIG. 85;

FIG. 87 shows the structure of another magnetic tape travelling systemin a conventional VTR; and

FIG. 88 shows the structure of the tension control system in the VTRshown in FIG. 87.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be explained hereinunder withreference to the accompanying drawings.

FIG. 1 shows a first embodiment of a magnetic recording and reproducingapparatus according to the present invention. In FIG. 1, a rotary drum51 with a magnetic tape 50 wound therearound accommodates two magneticheads 52a and 52b. The magnetic tape 50 is drawn out of a feed reel 53and wound around a take-up reel 54. Both reels 53, 54 are driven bymotors 55 and 56, respectively. In order to feed the magnetic tape 50 inthe direction of the travel at a constant speed, a capstan 57 and apinch roller 58 for clamping the magnetic tape 50 therebetween areprovided. The capstan 57 is driven by a capstan motor 59. In order towind the magnetic tape 50 around the rotary drum 51 at a predeterminedinclination angle, slant poles 60a and 60b are provided on the entranceside and the exit side, respectively, of the rotary drum 51.

The present invention is characterized in that a tape drawing actuator61 and a tape tension actuator 62 are provided on the exit side and theentrance side, respectively, of the rotary drum 51.

The tape drawing actuator 61 includes a movable tape pass roller 63which comes into contact with the magnetic tape 50, and a roller arm 64for holding the pass roller 63 is rocked by a driver 65. The rockingangle of the roller arm 64 is detected by a position sensor 66.

Fixed tape pass rollers 67 and 68 are provided on both sides of thetrajectory of the movable tape pass roller 63, and the gap between thefixed taped pass rollers 67, 68 is so set as to allow the movable tapepass roller 63 to pass therethrough. In this embodiment, the movabletape pass roller 63 passes the intermediate point of the fixed tape passrollers 67, 68 and at this time the gap between the movable tape passroller 63 and the fixed tape pass roller 67 is equal to the gap betweenthe movable tape pass roller 63 and the fixed tape pass roller 68.

Similarly to the tape drawing actuator 61, the tape tension actuator 62also includes a movable tape tension roller 69, a roller arm 70, adriver 71 and a position sensor 72, and fixed tape pass rollers 73 and74 are provided on both sides of the trajectory of the movable tapetension roller 69.

Principle of Operation of High-speed Superior Reproduction

FIG. 2 is a perspective view explaining the principle of the operationat the time of high-speed superior reproduction.

In FIG. 2, the speed of each part of the apparatus and the speed of themagnetic tape are schematically shown, wherein V_(A) is the speed of themagnetic tape 50 on the rotary drum 51, V_(B) is the moving speed of themovable tape pass roller 63 of the tape drawing actuator 61 and V_(C) isthe speed of the magnetic tape 50 driven by the capstan motor 59 or thetake-up reel motor 56.

High-speed superior reproduction is an operation of intermittentlyreproducing a picture while causing the tape at a speed for any giventimes as high as the normal speed. Conventionally, the head is caused tofollow the track only by the head actuator during this high-speed tapetravel, so that the high speed which enables reproduction is limited.

In the present invention, in order to solve this problem, the tapedrawing actuator 61 and the tape tension actuator 62 provided on theexit side and the entrance side, respectively, of the rotary drum 51,are differentially operated so as to produce a period in which thetravelling speed of the magnetic tape 50 is relatively low with respectto the magnetic head 52 even during high-speed tape travel. Sincehigh-speed reproduction is carried out in this period, reproduction witha good quality is enabled even during high-speed tape travel.

It is now assumed that the positional relationship between the fixedtape pass rollers 67, 68 and the movable tape pass roller 63 is such asthat schematically shown in FIG. 3. In FIG. 3, the gaps d' between thetwo fixed tape pass rollers 67 and 68 is equal to the diameter d of themovable tape pass roller 63.

A static system will first be considered because it is easier tounderstand. It is here assumed that one end of the magnetic tape 50 isfixed and the movable tape pass roller 63 is moved by a distance Δxwithin a time Δt, as shown in FIG. 3. An arbitray point D₀ on the freeend side of the magnetic tape 50 is moved to the point D₁ which is 2×Δxdistant from the point D₀. Therefore, the moving speed of the point D₀at that time is 2 times as high as that of the movable tape pass roller63. In other words, if it is assumed that the speed of the movable tapepass roller 63 is V_(B), the speed of the free end side of the magnetictape 50 is 2×V_(B). Since the movable tape pass roller 63 must passthrough the gap between the two fixed tape pass rollers 67 and 68 fortape loading, as is clear from FIG. 1, the following relationship musthold:

    d'>d·

However, if the difference between d and d' is Δd, Δd is preferably assmall as possible. This is because as Δd becomes larger, theabove-described linearity of the speed of the free end side of themagnetic tape 50 and the moving speed of the movable tape pass roller 63is disturbed more and the controllability is deteriorated. Therefore, inthe explanation of the principle of this embodiment, it is assumed thatΔd=0 and the linearity holds, and in a later explanation, Δd will betaken into consideration.

The case in which the magnetic tape 50 is moved at a stationary speed bythe capstan motor 59 will next be considered. Since the fixed end of themagnetic tape 50 is considered to move at a speed of V_(C), the speedV_(A) of the other end of the magnetic tape 50 is represented asfollows:

    V.sub.A =V.sub.C +2×V.sub.B·

The fixed tape pass rollers 73, 74 and the movable tape pass roller onthe tape entrance side of the rotary drum 51 are also provided such thata similar relationship holds.

The relationship between the speed V_(B) of the movable tape passrollers 63 (the movable tape tension roller 69) and the speed V_(A) ofthe magnetic tape on the rotary drum 51 shown in FIG. 2 is as describedabove.

Returning to FIG. 2, when the tape speed V_(C) becomes higher than thedynamic track following (DTF) speed allowable to the head actuator inthe rotary drum 51, which has been explained in the known systems, themovable tape pass roller 63 is moved in the direction of the relaxationof the magnetic tape 50 and the movable tape tension roller 69 is movedin the direction of the stretch of the magnetic tape 50 so as to lowerthe speed of the magnetic tape 50. In other words, by differentiallyoperating the movable tape pass roller 63 and the movable tape tensionroller 69 in the opposite phases by the same amount, the speed V_(A) islowered to a speed which allows the head actuator DTF for a constantperiod. Thus, it is possible to prevent a change in tension by movingthe movable tape pass roller 63 and the movable tape tension roller 69in the opposite phases by the same amount.

A method of controlling the speed V_(A) of the magnetic tape 50 on therotary drum 51 to the speed which allows the head actuator DTF andnoiseless reproduction by driving the movable tape pass roller 63 andthe movable tape tension roller 69 by the tape drawing actuator 61 andthe tape tension actuator 62, respectively will now be described.

FIG. 5 schematically shows an example of a VTR recording format. If themagnetic tape speed at the time of normal-speed reproduction is v, v isrepresented by the following equation:

    v=fα (m/sec)

wherein f is the rotational frequency (Hz) of the rotary drum 50, and##EQU1## wherein T_(p) represents a track pitch and θ represents a trackangle.

If it is assumed that the tape speed V', which a conventional DTF servosystem composed of the head actuator accommodated in the rotary drum 51can follow, is n times as high as the normal speed, V' is represented bythe following equation:

    V'=nv (n is an integer)·

As described above, when V_(C) >V', in other words, at the time ofhigh-speed reproduction, the movable tape pass roller 63 and the movabletape tension roller 69 are moved in the opposite phases by the sameamount at a speed of V_(B) so as to intermittently lower the speed V_(A)of the magnetic tape 50 on the rotary drum 51 to the speed V' whichallows a conventional DTF system to follow. In this way, noiselessreproduction which is conventionally impossible in high-speedreproduction is intermittently enabled.

Additionally, the characteristics of the displacement angles and thetorques of the tape actuators 61, 62 have a slight nonlinearity, asshown in FIG. 6.

The tape drawing actuator 61 and the tape tension actuator 62 arepreferably driven at a speed V_(B) by a triangular signal having a dutyof 50% such as that schematically shown in FIG. 7A in order to prolongthe reproduction-possible period as much as possible with considerationof the reduction ratio of the tape speed on the rotary drum 51.

In this case, the speed V_(A) of the magnetic tape 50 on the rotary drum51 obtained from the above equation

    V.sub.A =V.sub.C +2×|V.sub.B |

is such as that as schematically shown in FIG. 7C.

In FIG. 7C, if the tape speed V_(A) on the rotary drum 51 is selected sothat V_(A) is V', which is the speed allowing the head actuator DTF,V_(A) takes the minimum value, as represented by the following equation,which is the most efficient,:

    V.sub.A (min)=V.sub.C -2×V.sub.B =V'·

In this case, since V_(B) is in the opposite direction in FIG. 4, it isrepresented by -V_(B). At this time, the noiseless reproduction-possibleperiod T', in other words, the period in which the rectangular waveV_(A) <V' in FIG. 7C must be at least the period which enables themagnetic head 52 to reproduce one screen, namely, not less than 1/fsecond. Therefore, in order to enable reproduction of not less than onescreen in the noiseless reproduction-possible period T', the one cycletime T of the rectangular wave shown in FIG. 7C must be an integralnumber of at least two times of the rotational frequency 1/f of therotary drum 51. In this way, the tape actuators 61, 62 are drivensynchronously with the rotation of the rotary drum 51.

From the explanation of the principle, it is understood thatintermittent noiseless reproduction is possible at the time ofhigh-speed reproduction. Full-time noiseless high-speed reproductionwhich is continuous without a pause of screen, although it is composedof a series of successive stop-frames, is also enabled by storing thenoiselessly reproduced screens in a picture memory and outputting thestored pictures in a period in which noiseless reproduction isimpossible.

Servo System for High-speed Reproduction

The servo system in the magnetic recording and reproducing apparatus forrealizing the above-described principle of operation will here beexplained. As is obvious from FIG. 1, the tape drawing actuator 61 andthe tape tension actuator 62 are composed of actuators which practicenot linear motion but arcuate motion, as explained in the principle ofoperation. When the arcuate motion is approximated to linear motion, anonlinear error is caused in this structure in principle. FIG. 8schematically shows the positional relationship between the movable tapetension roller 69 (the movable tape pass roller 63) and the fixed tapepass rollers 73, 74 (67, 68) in the first embodiment in order to showthis error. In FIG. 8, γ represents the length of the arm 70 (64) and βrepresents the displacement angle of the arm 70(64). The relationshipbetween the displacement angle β of the movable tape tension roller 69and the length of the drawn magnetic tape 50 when the relationship shownin FIG. 8 is satisfied is shown in FIG. 9. As shown in FIG. 9, in theideal state wherein Δd=0 mm, an approximate linearity is obtained, butthe larger Δd becomes, the more remarkable becomes the nonlinearity inthe area in which the movable tape tension roller 69 is close to thefixed tape pass rollers 73, 74 (in the region in which the displacementangle β is 0° to 10° C. in FIG. 9). Accordingly, in this embodiment, Δdis set at 1 mm in the system so that the nonlinearity is almostnegligible.

It is, however, the general case that the nonlinear error increases dueto the mechanical restriction of the tape deck or nonuniformity of themechanical setting accuracy, so that it is necessary to take thisnonlinear error into consideration in the control system. For example,as shown in FIG. 10, the nonlinear error is large in comparison withthat shown in FIG. 9. When the mechanical characteristic E introducedfrom a circuit represented by 75 in FIG. 11 is nonlinear as shown inFIG. 10, there is a risk of the nonlinear error exceeding the range inwhich it is possible to correct the tracing of the head actuator 76 inthe DTF control shown in FIG. 11. The present embodiment thereforerequires a DTF control system in a wider dynamic range with a higheraccuracy than in a conventional DTF control system.

To meet this requirement, in the present embodiment, the track range iscorrected not only by a head actuator having a narrow dynamic range butalso by tape actuators having a wide dynamic range.

FIG. 12 is a schematic block diagram of a servo system in the presentinvention.

FIG. 12 includes the concrete flow of signals in the apparatus shown inFIG. 1 which is subjected to high-speed reproduction control, DTFcontrol and tension control.

The structure of DTF control will be briefly explained in the followingdiscussion. An envelope signal reproduced by the magnetic heads 52a and52b is supplied to a DTF circuit. The DTF circuit obtains a trackingerror signal from the envelope signal and the high-frequency componentthereof is fed back to the head actuator 76, the low-frequency componentthereof is fed back to the tape drawing actuator 61 and the DC componentthereof is fed back to the capstan motor 59 or the reel motor 56. Inorder to prevent a tension change caused by the DTF operation of thetape drawing actuator 61, a driving signal for the tape drawing actuator61 is also supplied to the tape tension actuator 62 through an adder 91.

The structure of tension control will be briefly described in thefollowing discussion. A movable roller position signal for detecting theposition of the movable tape tension roller 69 and a driving signalsupplied to the tape tension actuator 62 are supplied to a tensionestimating device 92. The tension estimating device 92 estimates thetape tension on the movable tape tension roller 69 and outputs anestimated tension signal to a tension servo circuit 83. The tensionservo circuit 83 compares the estimated tension signal with a referencetension signal to obtain a tension error signal. The low-frequencycomponent of the tension error signal is fed back to the reel motor 55and the high-frequency component thereof is fed back to the tape tensionactuator 62.

The structure of high-speed reproduction control will be brieflyexplained in the following. A capstan FG signal (or a reel FG signaloutput while the reel motor is driven, for example at the time ofhigh-speed reproduction) which indicates the tape travelling speed and adrum PG signal are supplied to a superior reproduction signal generator80. The superior reproduction generator 80 generates a superiorreproduction signal for operating the tape drawing actuator 61 and thetape tension actuator 62 from these two signals.

The details of each control will be described later.

The operation of the servo system will be explained in the followingdiscussion. Normal-speed reproduction will first be explained. When themagnetic tape 50 travels at a normal reproducing speed, the superiorreproduction signal generator 80 generates no correction pattern, sothat the tape drawing actuator 61 is fixed at a predetermined position.The position of the tape drawing actuator 61 may preferably be eithermechanically fixed or electrically fixed of a position controller with aclosed loop constituted of a position sensor (not shown) provided on thetape drawing actuator 61.

The tape tension actuator 62 is fixed to a predetermined position in thesame way as the tape drawing actuator 61, and exerts tension control forsuppressing the change in the tension of the magnetic tape 50 andmaintaining the tension at a constant value by a closed loop.

Since the tension control system is constituted by a closed loop, asdescribed above, control in a wider frequency band than a conventionalmechanical tension control is enabled and the performance of the tensioncontrol system is enhanced.

The details of the structure of the principle of tension control will bedescribed later.

Since the DTF operation in the range in which the speed of the magnetictape 50 is correctable by the head actuator 76 is completely the same asthat in conventional high-speed superior reproduction, an explanationthereof will be omitted. In this case, the superior reproduction signalgenerator 80 generates no signal, either.

However, the present embodiment is different from the known systemsbecause a tracking error is corrected by the cooperation of the headactuator 76 and the tape drawing actuator 61, so that DTF control havinga wide dynamic range is realized.

The operation of the servo system in a high-speed range in which thespeed of the magnetic tape 50 cannot be corrected by the head actuator76, which is the main part of the present invention, will now beexplained. When the apparatus is operated at a high speed which makesthe correction of the speed of the magnetic tape 50 by the head actuator76 impossible, noise bars or mosaics are displayed in the reproducedscreen in a conventional apparatus.

In the present embodiment, by operating the tape drawing actuator 61 andthe tape tension actuator 62 in accordance with the above-describedprinciple of operation, the speed of the magnetic tape 50 on the rotarydrum 51 is periodically lowered to a range in which the speed of themagnetic tape 50 is correctable by the head actuator 76. While themagnetic tape speed is in the range which enables the head actuator 76to correct the tape speed, in other words, in the reproduction-possibleperiod T', the amount of relative positional deviation between therecording track on the magnetic tape 50 and the magnetic head 52, namelytracking error, is corrected by a DTF control system which will bedescribed in detail in FIG. 12. A tracking error signal is obtained bythe known wobbling method, pilot method or the like. In this way, it ispossible to obtain a good reproduced picture without a noise caused byoff-track in the reproduction-possible period T'.

The reproduction-possible period T' is at least 1/f second, as describedin the explanation of the principle.

A superior reproduction signal for driving the tape drawing actuator 61and the tape tension actuator 62 is output from the tape superiorreproduction signal 80. The superior reproduction signal 80 detects thespeed of the magnetic tape speed which cannot be corrected by the headactuator 76 from the inputs of a tape speed signal such as a capstan FGsignal and a drum PG signal. On the basis of the principle described inthe explanation of the principle, the superior reproduction signalgenerator 80 outputs a driving voltage pattern for operating the tapedrawing actuator 61 and the tape tension actuator 62 so as to form aspeed pattern such as that shown in FIG. 7C. In a period other than thereproduction-possible period T', since no reproduced picture isobtained, if a good picture reproduced in the reproduction-possibleperiod T' is stored in a picture memory or the like in every cycleperiod, and the stored picture is output in a period other than thereproduction-possible period T', continuous high-speed reproduction isenabled. By this operation, a good reproduced picture free from noise,which is impossible in a conventional servo system, is continuouslyobtained, although it is composed of a series of successive stop-frames.

As described above, since the tape tension actuator 62 constantly keepsacting by a closed loop in a tape tension servo system in a wider rangethan a conventional mechanical actuator, the magnetic tape 50 ismaintained at the optimum tape tension in any state. By virtue of thiseffect, the magnetic recording and reproducing apparatus of the presentembodiment enables a good reproduced picture to be obtained in a widetape speed range from a low speed to a high speed.

The tape actuators 61, 62 may practice arcuate motion, as shown in FIG.13.

DTF Control

The operation of DTF control according to the present embodiment will beexplained in the following.

FIG. 14 is a block diagram showing an example of DTF control. In thepresent embodiment, a tracking error signal is detected from areproduction signal supplied from the magnetic head 52 in a pilot systemshown in the related art, and the head actuator 76 and the tape drawingactuator 61 are electrically coupled for tracking control. In otherwords, a two-stage coupling control system is adopted in the presentembodiment.

In FIG. 14, the DTF control outputs from the actuators 76 and 61 areadded to the target track position by an adder 85 and a tracking errorsignal is supplied to both actuators 76 and 61 through a compensator 86.

The output of the compensator 86 is directly supplied to the headactuator 76 and simultaneously supplied to the tape drawing actuator 61through a head actuator equivalent circuit 87, a compensator 88 and anadder 89. Therefore, the output of the equivalent circuit 87 indicatesthe value estimated by the head actuator 76. A signal for superiorreproduction is supplied to the other input terminal of the adder 89.

The tension control system includes the tension estimating device 92 andthe tension servo circuit 83 shown in FIG. 12. A tension estimatingsignal is supplied from the tension estimating device 92 to the tensionservo circuit 83. A driving signal supplied to the tape drawing actuator61 of the DTF control system is supplied to an adder 91 together withthe output of the tension servo circuit 83.

The output of the adder 91 is supplied to the tape tension actuator 62and output to the tension estimating device 92 for outputting anestimated tension which the tension roller of the tape tension actuator62 receives from the tape. The output of the tension estimating device92 is supplied to a subtracter 90.

The tension estimating device 92 electrically simulates the relationshipbetween the input voltage of the tape tension actuator 62 and thedisplacement of the tape tension roller 69 by using the (inputvoltage)/(displacement) transfer characteristic in this embodiment.

Such a two-stage coupling control system is known, for example, asdisclosed on pp. 203 to 208 of the transactions of Optical MemorySymposium '85 held on Dec. 12 to 13, 1985. In the field of optical disktracking control, it is known as a control in a dynamic range.

In the field of tracking control of a VTR, however, a tracking error isconventionally corrected only by the head actuator 76 accommodated inthe rotary drum 50, which makes such a two-stage coupling control systeminapplicable. In the present embodiment, since the tape drawing actuator61 is newly provided as a tracking error correcting device, applicationof a two-stage coupling control system is possible, so that DTF controlin a wide frequency band and a wide dynamic range with a high accuracyis enabled.

In the embodiment shown in FIG. 14, the present embodiment is applied toa digital VTR. In a digital VTR, since the amount of recordinginformation increases, high-density recording by narrowing the trackpitch is essential in order to meet the demand for a higher picturequality, multifunctions, long-time recording and the like. The recordingtrack generally has a nonlinearity of a track (hereinunder referred toas "track rolling") mainly caused by a mechanical factor. Since thetrack pitch becomes smaller than the amount of track rolling with such areduction in the track width, in order to exactly trace the narrowtrack, DTF control having a controlled region at least 10 times as largeas the fundamental frequency of the track rolling is required. Thefundamental frequency of track rolling depends upon the rotationalfrequency of the rotary drum. For example, when the rotational frequencyof the rotary drum is 1,800 rpm, the DTF control system is required tohave a controlled region of not less than 300 Hz.

In order to have a wide controlled region, the head actuator 76 isrequired to have a good controllability. In this embodiment, anelectromagnetic actuator shown in FIG. 15 is adopted.

The magnetic head 52 is supported by a coil bobbin 94 through a leafspring 93, and an exciting coil 95 is wound around the coil bobbin 94.

The coil bobbin 94 is axially and movably supported at both ends by acylindrical yoke 98 and discal yokes 99, 100 through gimbal springs 96,97. A mounting member composed of a polymer material is provided at eachjoint between the gimbal spring 96 (97) and the coil bobbin 94.

Within the coil bobbin 94, cylindrical permanent magnets 102, 103 arefixed between the yokes 99 and 100, and a center yoke 104 is providedbetween both permanent magnets 102, 103.

Thus, the head actuator 76 having the above-described structure can movethe magnetic head 52 as desired by appropriately controlling theexciting current applied to the exciting coil 95 in the same way as in aconventional actuator shown in FIG. 85.

As is clear from FIG. 15, a head position detector 105 constantlydetects the position of the magnetic head 52 optically orelectromagnetically.

In FIG. 15, although a bimorphous cell or other elements may be used asthe head actuator 76 so long as it has a good controllability, sincethis embodiment is applied to a publicly used digital VTR, anelectromagnetic actuator is adopted with importance attached toinexpensive and high reliability characteristics. Even if anelectromagnetic actuator is used, coexistence of DTF controllability andsuperior reproducibility is impossible, as described in the knownsystems. The electromagnetic actuator in this embodiment has a structuregiving priority to DTF controllability. By increasing the elasticmodulus of the gimbal springs 96, 97 shown in FIG. 15, the primarymechanical resonance frequency is heightened, for thereby obtaining acharacteristic that the phase is flat 0° up to a frequency of about 1KHz. However, when the elastic modulus of the gimbal springs 96, 97 isincreased in this way, the resonance peak gain is increased, for therebydeteriorating the controllability. To prevent this, in this embodiment,the position information on the movable portion of the head actuator isdetected by the head position detector 105, as shown in FIG. 15. Theposition signal and the driving voltage for the head actuator 76 areinput to a speed estimating device composed of a circuit whichelectrically simulates the (input voltage)/(displacement) transfercharacteristic of the head actuator 76, and the speed of the movableportion of the head actuator 76 is estimated. The estimated speed isnegatively fed back to the exciting coil 95 for electrical damping.Thus, the head actuator 76 functions as an actuator having a goodcontrollability up to a high frequency band.

By using such an actuator as the head actuator 76, a DTF control systemwhich is capable of DTF control in a wide frequency band with a highaccuracy is indeed realized, but since the elastic modulus of the gimbalsprings is increased as a result of attaching importance to DTFcontrollability, a large current is required when the actuator is drivenat a large amplitude, and problems, such as the generation of heat atthat time, limit the tolerable amplitude to a narrow range. In otherwords, the dynamic range is narrowed.

As a countermeasure, in the present embodiment, the head actuator 76compensates mainly for a small amplitude in a high-frequency band of atracking error, while the newly provided tape drawing actuator 61compensates for a large amplitude in a low-frequency band of a trackingerror. The tape drawing actuator 61 is designed as a voice coil typeelectromagnetic driven actuator which has no support spring, as shown inFIG. 16, so as to have a large low-frequency gain. The tape drawingactuator 61 has a similar structure to a magnetic circuit which has beenput to practical use as a swing arm actuator, which is a tracking armactuator of a hard disk driving apparatus. FIG. 17 shows the magneticcircuit of the tape drawing actuator 61, FIG. 18 shows the principle ofdriving the tape drawing actuator 61 and FIGS. 19(a1), (a2), and (a3),and 19(b1), (b2) and (b3) are sectional views of the tape drawingactuator 61 according to first and second embodiments.

The roller arm 64 is rotatably supported by a yoke 106 of the driver 65,and a permanent magnet 107 is fixed to the yoke 106 as illustrated inFIGS. 19(a1), (a2) and (a3).

As is clear from FIGS. 17 and 18, the permanent magnet is magnetizedsuch that the directions of magnetization are opposite on left and rightsides. A movable coil 108 is fixed to one end of the roller arm 64 andis movable perpendicularly relative to the direction of themagnetization of the permanent magnet 107, as illustrated in the FIG.19(a) embodiment.

In this way, by supplying an appropriate current to the coil 108, it ispossible to rotate the movable tape pass roller 63 to any given positionby the electromagnetic action of the coil 108 and the permanent magnet107.

In the FIG. 19(b) embodiment, permanent magnet 107 is fixed to one endof roller arm 64 and coil 108 is fixed to yoke 106. The manner in whichthe tape drawing actuator of the FIG. 19(b) embodiment functions issimilar to and would be understood in view of the FIG. 19(a) embodiment,and thus is not described further.

In FIGS. 17, 18 and 19 the magnetized tape drawing actuator 61, is shownand it is preferable that the tape tension actuator 62 has a similarstructure.

FIG. 20 shows an example of an actuator roller position sensor. In FIG.20, a rotary shaft 109 of the actuator is provided with a mirror surfaceportion 109a. The light from a light emitting device 110 is reflected bythe mirror surface portion 109a and received is by a light receivingdevice 111.

The light emitting device 110 is preferably composed of a combination ofa laser oscillator and a collimator or the like.

As is obvious from FIG. 20, the rotational angle of the rotary shaft ofthe tape drawing actuator 61 is detected by the light receiving device111, for thereby making it possible to know the position of the movabletape pass roller 63.

The torque characteristic of the tape actuator having theabove-described structure is almost flat irrespective of thedisplacement angle, as shown in FIG. 6. The (displacementangle)/(voltage) frequency characteristic of a tape actuator is freefrom a mechanical resonance up to a high frequency band, as shown inFIG. 21, so that the actuator has a good controllability.

In the present embodiment, the head actuator 76 and the tape drawingactuator 61 are controlled by a common control system for correcting atracking error. The coupling frequency of the two-stage coupling control(the frequency at which the gains of the control loops of both actuatorsbecome equal) is determined as follows. The fundamental frequency of atracking error caused by a nonlinearity error due to the mechanicalcharacteristic E during high-speed superior reproduction which requiresa wide dynamic range is mainly determined by the frequency of thedriving pattern of the tape drawing actuator 61. Since the tape drawingactuator 61 is driven by a frequency synchronous with the rotationalfrequency of the drum, e.g., a triangular signal having a frequency of XHz during high-speed superior reproduction, as described above, theamplitude of a low-frequency component of a tracking error of not morethan X Hz becomes large, so that this component must be mainly correctedby the tape drawing actuator 61 having a wide movable range.

For this reason, the coupling frequency is set in the vicinity of X Hzin this embodiment. In this embodiment, X=7.5. In other words, byselecting the common frequency in this way, it is possible to assign ahigh-frequency component of a tracking error mainly to the head actuator76, which has a high high-frequency followability and a low-frequencycomponent of a tracking error mainly to the tape drawing actuator 61which has a large low-frequency torque and a high low-frequencyfollowability. In this way, in a two-stage coupling control system, twoactuators simultaneously follow one controlling target and thecontrollability for following the target is divided into two partsdepending upon the frequency band. Therefore, when the phase differenceof the actuator control systems is 180° at the coupling frequency, thetotal gain becomes--∞dB (antiresonance is caused). In this embodiment,the system is stabilized by the structure in which the movement of thetape drawing actuator 61 follows the movement of the head actuator 76and the amount of phase compensation at the coupling frequency isdetermined by pole-positioning.

In the control system shown in FIG. 14, since the DC component or thelow-frequency component of a tracking error signal is corrected only bythe tape drawing actuator 61, the amount of correction is sometimesrestricted. FIG. 22 shows an example of a control system in which thecorrection of a low-frequency component is assigned to the tape drawingactuator 61 and the capstan motor 59 or the reel motor 56. In thiscontrol system, the position of the movable tape pass roller 63 isdetected and the DC component of the deviation of the detected positionfrom the reference position (e.g., the center point of the movablerange) is fed back to the capstan motor 59 or the reel motor 56. By thisstructure, the two actuators 76, 61 of the two-stage coupling system areconstantly operated within the respective movable ranges.

Operation of DTF control

The principle of DTF control has been described above. The operationthereof will now be described with reference to the block diagram shownin FIG. 23, which is obtained by rewriting the DTF control system shownin FIG. 14.

FIG. 23 is a block diagram of DTF control in this embodiment of thepresent embodiment which is represented by transfer functions. Thesymbol s represents a Laplace operator.

In FIG. 23, the reference numeral 120 represents a transfer functioncircuit as a means for separating a tracking error signal into alow-frequency component and a high-frequency component. Thehigh-frequency component is fed back to the DTF control system and alow-frequency component is fed back to the capstan motor 59 or the reelmotor 56. The reference numeral 86 is a transfer function circuitrepresenting a compensation filter, which is a primary low pass filterrepresented by the following equation: ##EQU2## The reference numeral121 is a transfer function representing the gain of an amplifier foradjusting the servo gain for DTF control. The head actuator 76 isrepresented by a transfer function circuit representing the (inputvoltage)/(displacement) transfer characteristic. The symbols KH.sub.τ,R_(T), m_(H), C_(H) and R_(H) are transfer functions representing atorque constant, coil resistance, mass of the movable portion, viscositycoefficient and elastic modulus, respectively. The reference numeral 87is a transfer function circuit representing the filter electricallysimulating the frequency characteristic of the head actuator 76 andrepresents an equivalent circuit of the head actuator 76. The referencenumeral 88 is a transfer function circuit representing a compensator,which is a read lag filter represented by the following equation;##EQU3##

The reference numeral 122 is a transfer function representing a gain ofan amplifier. The tape tension actuator 61 is represented by a transferfunction circuit for the (input voltage)/(displacement angle)characteristic. The symbols KH₉₆, R_(T), J_(T) and C_(T) are transferfunctions representing a torque constant, coil resistance, inertia ofthe rotary portion and viscosity coefficient of the rotary portion,respectively. The reference numeral 75 is a nonlinear function of therotational angle β which represents the relationship between thedisplacement angle of the tape drawing actuator 61 and the amount ofdisplacement thereof in the direction of the width of the recordingtrack, shown in FIG. 10. If the tape drawing actuator 61 is used in anarrow range in which the rotational angle is restricted, for example,in the vicinity of the point at which the displacement angle of the dtand the amount of displacement thereof in the width of the recordingtrack are β₀, f₃ (β) can be approximated to ##EQU4## A position sensor66 is represented by a transfer function circuit for the gain of thesensor representing the (input voltage)/(displacement angle)characteristic. The reference numeral 124 is a transfer function circuitrepresenting a compensation filter for stabilizing the position controlloop for electrically fixing the position of the tape drawing actuator61. The compensation filter is a read lap filter represented by thefollowing equation: ##EQU5## The reference numeral 125 is a transferfunction representing the gain of an amplifier for determining the loopgain of the position control loop.

A tracking error signal obtained from a reproducing signal of themagnetic head by a pilot system is passed through the low pass filter120 in which the cut-off frequency is several Hz, and the low-frequencycomponent is fed back to the capstan motor 59 or the reel motor 56.Simultaneously, the phase of the tracking error signal is compensated bythe compensator 86 composed of a primary delay filter having a lowfrequency in which the cut-off frequency is several Hz and the trackingerror is amplified by the amplifier 121. The amplified tracking error issupplied to the drive amplifier (not shown) of the head actuator 76 soas to drive the head actuator 76. As a result, the magnetic head 52 ismoved and the first control loop is closed. The output of the amplifier121 is input to the head actuator equivalent circuit 87, which is afilter electrically simulating the (input voltage)/(displacement)characteristic of the head actuator 76, and a secondary delay filter inthis embodiment in which the cut-off frequency is the primary resonancefrequency of the head actuator 76. The output signal is supplied to thecompensator 88 so that the two-stage control loop including the firstcontrol loop is stabilized. For example, this signal is supplied to thecompensator 88 composed of the filter represented by the followingequation: ##EQU6## wherein the transfer functions T₂ and n₂ are sodetermined that all the poles of the control system shown in FIG. 24 aredisposed in the region of the negative real axis (convergentpole-positioning). The output of the compensator 88 is amplified by theamplifier 122 to a gain which enables the output to couple with thefirst loop at X Hz and is supplied to a drive amplifier (not shown)through an adder 123 of the position control loop of the tape drawingactuator 61 and the adder 89 for a signal for superior reproduction soas to drive the tape drawing actuator 61. As a result, the magnetic tape50 is moved in the direction of travel through the mechanicalcharacteristic E circuit 75 shown in FIG. 14 and the second control loopis closed so as to correct the tracking error.

In this embodiment, by the above-described two electrically coupledtwo-stage coupling control loop, DTF control in a wide frequency bandand a wide dynamic range with a high accuracy is realized. The open loopcharacteristic thereof is shown in FIG. 25.

In the system shown in FIG. 23, a part of the DC component of a trackingerror is corrected by the tape drawing actuator 61. Since the movablerange for the tape drawing actuator 61 is limited, the remaining DCcomponent is fed back to the capstan motor 59 or the reel motor 56.Naturally, the servo gain at this time is so constituted as to be higherthan that of the two-stage coupling control system composed of only thetape drawing actuator 61.

According to this structure, since the two actuators 76, 61 of thetwo-stage coupling control system are almost exempt from the correctionof the DC component, they can constantly operate in the movable range.

However, according to this system, since DTF control is exerted byfeedback of the low-frequency component of a tracking error to the tapedrawing actuator 61 and moving the magnetic tape 50 in the direction oftravel, change in tension is caused in principle. To prevent this, inthis embodiment, by applying the driving voltage for the tape drawingactuator 61 also to the tape tension actuator 62, as shown in FIG. 14,the two tape actuators 61, 62 are differentially operated in any mode(e.g., normal-speed reproduction mode or high-speed superiorreproduction mode). This differential action is aimed at suppression ofchange in tension caused by the tracking operation of the tape drawingactuator 61. However, only when the electrical and mechanicalcharacteristics of the two tape actuators 61, 62 are completely equal,the exact suppression is possible. Actually, even if an equal voltage isapplied to the two tape actuators 61, 62, it is generally impossible tooperate the two tape actuators 61, 62 in completely the same way due tothe nonuniformity of mechanical and electrical characteristics and achange in tension is inevitable. In the present embodiment, the changein tension is corrected to the optimum tension value in any mode by atension control system by a closed loop which will be described indetail hereinunder.

Operation of Tension Control System

The operation of a tension control system in this embodiment will now beexplained.

In a conventional tension control, when the force of the spring 22 isbalanced with the tape tension, the amount of displacement of thetension control arm 21 is regarded as the tension, and the amount ofdisplacement is fed back to the reel motor 6 as the detected tensionvalue, as shown in FIG. 81.

Strictly speaking, however, it is up to the spring resonance frequencyof the tension control arm 21 which is supported by the spring 22 thatthe amount of displacement of the tension control arm 21 supported bythe spring 22 is proportional to the tape tension, and beyond the springresonance frequency, the phase of the change in the tension applied tothe tension control arm 21 is deviated from the phase of the change inthe position of the tension control arm 21. Actually, the phase isshifted by 90 degrees at the spring resonance frequency and by 80degrees at a higher frequency. As a countermeasure, in a conventionaltension control system, the controlled region is limited by the phaseshift of the spring support system including the tension control arm 21.This means that the tension detectable by the tension control arm 21 islimited to the frequency band of not higher than the spring resonancefrequency of the spring support system including the tension control arm21. It will naturally be considered to lighten the tension control armor increase the spring constant in order to heighten the springresonance frequency. However, there is a limitation in lightening thetension control arm, and if the spring constant is increased, thetension control arm 21 does not move much even if there is a change intension, for thereby lowering the detection accuracy.

In this embodiment, the tension control arm is not mechanicallysupported by a spring. However, the tension control area is supported bywhat is called electrically supported by a spring by electrical positioncontrol. In addition to the electrical position control, the frequencyband in which the tension is detectable is enlarged and, as a result,tension control with a high accuracy is also enabled. This method isshown in FIG. 26.

FIG. 26 is a block diagram of a tension control system in thisembodiment. In FIG. 26, the reference numeral 126 represents a circuitfor an electrical characteristic of the tension actuator 62 representingthe (generated torque)/(input voltage) characteristic. The referencenumeral 127 represents a circuit for a mechanical characteristic of thetension actuator 62 representing the (displacement angle)/(suppliedvoltage) characteristic. The reference 128 represents a circuit for atape mechanical characteristic F which is determined by variouscharacteristics such as the length of the arm 70 of the tape tensionactuator 62, the geometrical positional relationship between the tapetension roller 69 and the fixed tape pass rollers 73, 74, the(stress)/(strain) characteristic of the magnetic tape 50 in thelongitudinal direction and the sectional area of the magnetic tape 50.The reference 129 represents a circuit for a travel path mechanicalcharacteristic which is determined by various characteristics such asthe geometrical positional relationship between the tape tension roller69 and the fixed tape pass rollers 73, 74, the balance of the forces ofthe magnetic tape 50 and the tape tension roller 69 and the geometricalpositional relationship between the tape tension roller 69 and therotary shaft of the driver 71 for the tape tension actuator 62.

The reference numeral 130 represents a position controller forelectrically fixing the tape tension actuator 62 at the referenceposition. The reference 131 represents a driver for driving the tapetension actuator 62. The reference numeral 132 represents a tensionestimating device for electrically estimating the tape tension from thedriving voltage or driving current and the detected amount ofdisplacement output from the position sensor 72. The reference numeral133 and 134 represent compensators for feedback of the differencebetween the estimated tension value output from the tension estimatingdevice 132 and the reference tension value, namely, the amount oftension change caused by external disturbance to the tape tensionactuator 62 and the feed reel motor 55 so as to stabilize the loop. Adriver 135 drives the feed reel motor 55.

The reference numeral 136 represents a circuit for a tape mechanicalcharacteristic G representing the tape tension changing characteristiccaused by a change in the rotational angle. A subtracter 137 calculatesthe difference between the estimated tension value output from thetension estimating device 132 and the reference tension value. An adder138 adds the position control signal from the position controller 130 tothe tension control signal from the compensator 133.

In FIG. 26, the total tension of the magnetic tape travelling system isobtained by adding an external tension disturbance (an externaldisturbance caused by the dynamic friction received by the tape from theshaft and the drum and a change in the frictional coefficient of thetape and an external disturbance in the longitudinal direction of thetape) to the sum of the change in the tension value caused by the changein the rotational angle of the tape tension actuator 62 and the tensionchange caused by the change in the rotational angle of the reel motor55. On the basis of the thus-obtained tension, the tape tension actuator62 is displaced.

The driver 71 for the tape tension actuator 62 has already beendescribed with reference to FIG. 17, but it will be explained in moredetail hereinunder. The magnetic circuit is closed by the yoke 106 andthe permanent magnet 107 which is magnetized in the directionperpendicular to the rotating surface of the movable coil 108 and inwhich the direction of magnetization is divided into two oppositedirections with respect to the rotary arcuate direction. Therefore, ahigh magnetic flux density is obtained in the perpendicular direction tothe rotating surface of the movable coil 108. When a current is appliedto the movable coil 108, the movable coil 108 is rotated by the forcecaused at the portions indicated by the reference numerals 108a, 108b inFIG. 18 according to the Fieming's left-hand rule. Furthermore, in orderto measure the amount of displacement of the arm 70 or the tape tensionroller 69, an optical position sensor such as that shown in FIG. 20 isprovided, as described above.

The structure shown in FIG. 20 is suitable to the case in which thefundamental wave of tension change is a high frequency and in a widedynamic range. It goes without saying that in the case in which thefundamental wave of tension change is a comparatively low frequency andhas a small amplitude, it is possible to use an LED, which is cheaper,as the light emitting device 110 and a separation detector, which ischeaper, as the light receiving portion 111. It is also possible todetect the position by a magnetic device, which is cheaper, as shown inFIGS. 27 and 28.

2 In FIG. 27, a Hall element 140 is provided on the arm integrally withthe exciting coil 108 and the Hall element can electrically detect therotational position of the tape tension roller 63 in cooperation withthe permanent magnet 107.

In FIGS. 28(a) and (b), a Hall element 141 is provided on the excitingcoil 108 on the opposite side of the rotary shaft 109, and the permanentmagnet 142 fixed for position detection and the Hall element 141 canelectrically detect the position of the tape tension roller 63 incooperation with each other.

By the above-described structure, the tape tension actuator 62 is drivenby an electromagnetic force and can detect its own amount ofdisplacement.

In this embodiment, since the tension estimating device 132 constituteswhat is called a co-dimensional observer (hereinunder referred to as"tension estimating device") in the modern control theory whichelectrically simulates the transfer characteristic (drivingcurrent/displacement) of the tape tension actuator 62, it is possible todetect the tape tension applied to the tape tension actuator 62 in awider frequency band in comechanon with the conventional mechanicaltension detector such as that shown in FIG. 81.

The above-described principle will be explained in more detail. FIG. 29shows the transfer functions of the tension estimating device 132.

FIG. 29 is obtained by converting the block diagram of the tensioncontrol system shown in FIG. 26 into the transfer functions of thecontrol theory. The symbol s is a Laplace operator.

The reference numeral 126 represents a transfer function including thecoil resistance R in the tape tension actuator 62 and the force constantK.sub.τ of the electromagnetic driving portion, 127 represents atransfer function including the inertia J of the movable portion of thetape tension actuator 62 and the viscosity function C, 128 represents atransfer function indicating the transfer characteristic of the changein the tape tension with respect to the change in the rotational angleof the tape tension actuator 62, and 131 represents a transfer functionindicating the transfer characteristic which the tape tension imparts tothe tape tension actuator 62.

The reference numeral 130a represents a phase lead filter, which is acompensator for compensating a position error signal which is adifference between the position signal output from the position sensor72 of the position control group for electrically fixing the referenceposition of the tape tension actuator 62 and the reference positionsignal P_(N), and 130b represents the gain of an amplifier fordetermining the loop gain of a position control feedback loop. Thereference numeral 133a represents a high pass filter, which is a part ofthe compensator 133 for feeding back a comparatively high frequencycomponent in the controlled region in the tension control system to thetape tension actuator 62, and 133b represents the gain of an amplifierfor determining the loop gain of a feedback loop with respect to thetape tension actuator 62. The reference numeral 134a represents a lowpass filter, which is a part of the compensator 133 for feeding back acomparatively low-frequency component in the controlled region of thetension control system to the feed reel motor 55, and 134b is the gainof an amplifier for determining the loop gain of the feedback loop withrespect to the reel motor 55. The reference numeral 55a represents atransfer function including the coil resistance R_(L) and the torqueconstant K_(LZ), and 55b represents a transfer function including therotational inertia J_(L) of the reel motor 55. The reference numeral 136is a transfer function representing the (tape tension)/(angle)characteristic which indicates the influence of the change in the angleof the reel motor 55 on the tape tension.

The reference numeral 150 is a transfer function circuit electricallysimulating the transfer function 126, and 151 and 152 are transferfunction circuits electrically simulating the transfer function 127 bythe equivalent conversion of the control theory. The reference numeral153 and 154 are the feedback gains of the observer (tension controlsystem) which are fed back so as to converge the differences between theoutput of the position sensor 72 and the respective outputs of thetransfer function circuits 150, 151 and 152 on zero in order that thedynamic characteristics of the transfer function circuits 150, 151 and152 which electrically simulate the characteristic of the tape tensionactuator 62 agree with the characteristic of the actual tape tensionactuator 62. The reference numeral 155 is a transfer functionrepresented by the inverse characteristic of the transfer function 131.

In FIG. 29, when a driving voltage to be input to the tape tensionactuator 62 is input to the transfer function circuit 150 whichelectrically simulates the coil resistance R and the force constantK.sub.τ, the output b' of the tension estimating device 132 becomes theestimated value of the actual driving force b of the tension controlsystem. The transfer functions of the circuits 151 and 152 arecollectively represented by the following equation: ##EQU7## Since thetransfer function circuits 151 and 152 simulate the transfer function ofthe mechanical characteristic of the tape tension actuator 62, when theoutput b' of the transfer function circuit 150 is input, the output d'of the transfer function circuit 152 ought to be the estimated value ofthe rotational angle d of the tape tension actuator mechanicalcharacteristic circuit 127. However, the transfer function circuits 151and 152 are provided with integrators therewithin, and even if thetransfer functions are the same as the characteristic output from thecircuit 127 in the tape tension actuator 62 with respect to thefrequency characteristics, the dynamic characteristics thereof are notequal thereto due to a difference in the initial values of theintegrators. Therefore, the difference e between the actual amount ofdisplacement d" detected by the position sensor 72 and the estimatedvalue d' of the tension estimating device 132 is fed back at gains F₁and F₂, whereby the dynamic characteristics as well as the frequencycharacteristics agree with those of the actual tape tension actuator 62.

The above-described structure is well known as the structure of aco-dimensional observer in the modern control theory. It is in order tofreely determine the convergence of the observer that the signals arefed back in the two loops at the gains of F₁ and F₂ to the inputterminals of the transfer function circuits 151, 152 which include theintegrator (1/S in a Laplace conversion) in the model of the tapetension actuator 62. A co-dimensional observer to which the drivingvoltage and the displacement of an object of control are input isgenerally used to estimate the internal speed thereof. If the feedbackgains F₁, F₂ of the co-dimensional observer are adequately larger thanthe pole 156 of the observer in FIG. 30 (the negative real number islarge), in other words, if the values of F₁, F₂ are large (high gains),in the state in which the dynamic characteristic and the staticcharacteristic of the object of control agree with each other, it ispossible to estimate the tension. At this time, since the dynamiccharacteristic agrees with the static characteristic, the followingrelationship holds:

    d'≈d                                               (2)

FIG. 30 shows the pole-positioning of this control system. The referencenumeral 156 represents the pole of the tape tension actuator 62, 158represents the pole of the position control feedback loop of thiscontrol system, 159 represents the pole of the feedback loop to the reelmotor 55 of this control system, 160 represents the pole of the feedbackloop to the tape tension actuator 62 of this control system, and 157represents the pole of the tension estimating observer. The abscissarepresents a real number axis and the ordinate an imaginary number axis.

Since the transfer function circuit 150 does not include an integrator,the driving force b' is represented as follows:

    b'≈b                                               (3)

Since the dynamic characteristic of the object of control agrees withthat of the model in the observer, the speed and the acceleration aswell as the displacement agrees with those of the model. Therefore, theforce c' applied to the arm of the tape tension actuator 62, which isequivalent to M times of the acceleration is represented as follows:

    c'≈c                                               (4)

Since the sum of the driving force b and the torque a is the torque c inthe original tape tension actuator 62, as in the following equation;

    b+a=c                                                      (5)

the following relationship holds from the formulas 2 to 5:

    b'+a=c'

    b'-c'=a                                                    (6)

that is,

    a'=a                                                       (7)

This means that a' in the signal path in the observer represents thetorque caused by the tension, and that it is possible to detect thetorque caused by the tension by taking out a'.

The relationship between the tape tension and the torque which the tapetension applies to the mechanical part of the tension actuator is shownin FIGS. 31 and 32.

FIG. 31 schematically shows the balance of the forces of the tapetension roller 69 and the magnetic tape 50. In FIG. 31, the symbol K₁represents a modulus of longitudinal elasticity and C₁ represents theviscosity coefficient of the magnetic tape 50. T_(N) represents atension value and T_(G) represents an external tension disturbancevalue.

FIG. 32 shows the mechanical relationship between the positions of themovable tape tension roller 69 and the fixed tape pass rollers 73, 74and the length of the arm 70.

From the statical point of view, the force which the tape tension roller69 receives from the magnetic tape 50 is represented by 2 (T_(N)+T_(G)). However, since the actual magnetic tape 50 is not a rigid bodyand is considered as a viscoelastic body, it is necessary that the tapetension value also changes with time and position as parameters. One ofthe characteristics of this embodiment is that the length of the tapebetween the rotary magnetic head 52 which is used for tape tensioncontrol and the tension roller 69 which is the point of application forthe actual control is shortened so as to avoid the influence of thedynamic characteristic in the longitudinal direction of the tape as muchas possible. Actually, the magnetic tape 50 is wound around the tapetension roller 69 at a contact angle of not 180°, as shown in FIG. 31,but less than 180°, as shown in FIG. 32. If the contact angle isrepresented by 180°-2θ₁ (θ₁ is a positive angle), the force applied tothe tape tension roller 69 is represented by 2cosθ₁ (T_(N) +T_(G)). Asshown in FIG. 32, the tape tension roller 69 is connected to the rotaryshaft of the actuator driving portion 71 through the arm 70 having alength r, and the torque applied to the tension roller 69 by the tapetension is represented by the following equation:

    a=f.sub.8 (T.sub.N +T.sub.G)

    f.sub.8 =2r cos θ.sub.1                              (8)

Therefore, the relationship between the tape tension value aa (=T_(N)+T_(G)) containing the external tension disturbance and the torque awhich the tape tension applies to the actuator 62 shown in FIG. 29 isrepresented by the following equation:

    a=2r cos θ.sub.1 aa                                  (9)

On the other hand, the estimated tape tension value a' a' is obtainedfrom the estimated tape tension torque a' by multiplying a' by thereciprocal of f₈, as represented by the following equation: ##EQU8##

In this way, it is possible to obtain the tension by estimation.Additionally, when the observer is matched with the model, the tensionestimating capacity of the tension estimating device 132 depends uponthe two feedback gains F₁, F₂, and represented by the followingequation; ##EQU9## F₁ mainly determines the frequency which allows theestimation and F₂ mainly determines the stability of the observer loop.

FIG. 33 shows the tension estimating capacity of the tension estimatingdevice 132 in this embodiment. In this case, the external disturbanceestimating capacity is about 1 KHz.

The estimated tension aa' is compared with the reference tension T_(N),which is the optimum value of the tension, and the tension error,namely, the external tension disturbance value T_(G) is detected. Onlythe high-frequency component of the external tension disturbance valueT_(G) is taken out by the high pass filter 133a and fed back to the tapetension actuator 62 at a transfer function of f₅ which includes phasecompensation and amplification. Simultaneously, the low-frequencycomponent thereof is taken out by the low pass filter 134a and fed backto the feed reel motor 55 at a gain of G₆. The reason why the frequencyband is divided as described above is because the tape tension actuator62, which has a small mechanical time constant, is generally suitablefor the control in a high-frequency band but since the movable range islimited, it is impossible to control a change in the tension which has acontrolled value approximate to that for a direct current. In thepole-positioning of the transfer functions f₅ and f₆ shown in FIG. 30,for example, the points which are closer to the original point than tothe pole 157 of the observer (for example, about 1/10 of the pole 157 bythe real number) are selected for the pole 160 of the tension controlloop to the tape tension actuator 62 and the pole 159 of the tensioncontrol loop to the feed reel motor 55.

FIG. 34 shows the transient behavior of the estimated externaldisturbance at this time. The actual tension value T_(r) agrees with theestimated tension value T_(p) after a constant time.

In FIG. 34, the transient characteristic of the estimated tension valueT_(r) of the tension estimating device 132 and the actual tape tensionchange T_(p) from the start of operation is shown. The abscissarepresents a time and the ordinate a tension force.

FIGS. 35(a) and 35(b) show the open loop characteristic of the tensioncontrol system of this embodiment. In FIG. 35(a), the ordinaterepresents a gain and the abscissa represents a frequency. In FIG.35(b), the ordinate represents a phase and the abscissa represents afrequency.

The principle and the operation of the tension control system in thisembodiment have been explained above.

When the tension is controlled by the above-described method ofestimating the external tension disturbance, the estimated tension isexactly detected up to a much higher frequency than that substituted bythe amount of displacement of the tension control arm as in aconventional tension control mechanism, for thereby realizing tensioncontrol in a very wide frequency band.

Since loops are complicatedly intertwined in such tension control unlikein a simple feedback loop having one input and one output, a largeamount of operation is required. Although the integrator, amplifier,adder, subtracter or the like can naturally be constituted by an analogcircuit by using an operational amplifier or the like which produces fewoffsets and drifts, since such an amplifier is expensive and the circuitbecomes a large scale, it is desirable to digitally operate by amicrocomputer or the like.

FIG. 36 shows the structure of the hardware in the control system shownin FIG. 29 which is constituted by a microcomputer. It is possible torealize the control system having very little hardware, as shown in FIG.36.

In FIG. 36, the reference numeral 161 represents a sensor amplifier, 162represents an analog/digital converter for converting an analog signalsupplied from the sensor amplifier 161 into a digital signal and 163represents a high-speed operation circuit for digitally executing theestimation of a tension and compensation thereof by a microcomputer orthe like on the basis of the transfer functions shown in FIG. 29. Thereference numeral 164 represents a current/voltage converter for takingout the driving current for the tension control mechanism in the form ofa voltage and 165 represents an analog/digital converter for convertingthe analog output of the current/voltage converter 164 into a digitalsignal. The reference numerals 166, 167 represent digital/analogconverters for converting the result output from the high-speedoperation circuit 163 into an analog output. FIG. 37 shows an example ofa flowchart for the algorithm of the estimated tension which is computedby a digital operation by the high-speed operation circuit 163 in thestructure shown in FIG. 36. The integration factor Σ shown in FIG. 37 isrealized by the structure of the block diagram of FIG. 38.

As described above, according to this embodiment, since the tape tensionactuator 62 suppresses a tension change in the high-frequency band andthe feed reel motor 55 suppresses a tension change in the low-frequencyband, the tension control accuracy is enhanced and a tension controlsystem capable of tension control with a high accuracy in a widefrequency band and a wide dynamic range is realized.

In this way, according to the present embodiment, since the controlranges and the dynamic ranges of a DTF control system and a tensioncontrol system are enlarged by using DTF control and tension controlutilizing an external disturbance observer, good reproduction ispossible not only in a normal-speed reproduction mode but also in ahigh-speed superior reproduction mode.

Although the tape tension actuator 62 is disposed on the top side (onthe side of the rotary drum) of the VTR deck in this embodiment, it maybe provided on the back surface of the VTR deck with consideration ofthe limitation of the size of the VTR deck, as shown in FIG. 39. Asimilar effect is produced by a compact structure in which the magneticcircuit of the actuator is accommodated in the VTR deck.

Operation in High-speed Superior Reproduction

The operation of the apparatus at the time of high-speed superiorreproduction in which the speed of the magnetic tape 50 cannot becorrected by the head actuator 76 will now be explained as the main partof the present embodiment.

When a conventional apparatus is operated at a high speed at which thespeed of the magnetic tape 50 cannot be corrected by the head actuator76, a screen has noise bars or becomes a mosaic screen. In the presentembodiment, by operating the tape drawing actuator 61 and the tapetension actuator 62 in accordance with the above-described principle,the speed of the magnetic tape 50 on the rotary drum 51 isintermittently lowered to the speed at which the head actuator 76 cancorrect the speed of the magnetic tape 50, for example, the normalreproduction speed. In the period in which the speed of the magnetictape 50 is correctable by the head actuator 76, namely, thereproduction-possible period T' explained in the above principle, thecorrection of a tracking error is enabled by the above-describedtwo-stage coupling DTF control system in accordance with the presentembodiment even in the worst case in which, for example, the speedchanges by the mechanical characteristic shown in FIG. 10 and thetracking error pattern exceeds the range in which the head actuator 75can correct a tracking error. The reproduction-possible period T' is aperiod in which at least one picture is reproducible, namely, at leastm₀ /f (m₀ is an integer of at least 2) sec, as described above. Asuperior reproduction signal generator (not shown) outputs a signal forsuperior reproduction for driving the tape actuators 61, 62. In thisembodiment, a driving voltage pattern for digitally operating the tapeactuators 61, 62 is output so as to produce the speed pattern shown inFIG. 7 by inputting the tape speed information from the capstan portionsuch as a capstan FG signal and a drum PG signal on the basis of theexplained principle. The hardware structure of the superior reproductionsignal generator can be realized by simple digital circuits, but anexplanation thereof will be omitted here.

In a period other than the reproduction-possible period T', since noreproduced picture can be obtained, a good picture reproduced in thereproduction-possible period is stored in each cycle period, and duringthe period other than the reproduction-possible period T', the storedpictures may be output. By this operation, a good reproduced picturefree from noise, which is impossible in a conventional servo system, iscontinuously obtained, although it is composed of a series of successivestop-frames. As described above, the tape tension actuator 62 isconstantly operated by a tape tension servo in a wider range than by aconventional mechanical system. It goes without saying that the magnetictape 50 is therefore maintained at the optimum tension in any state.Thus, this embodiment of a magnetic recording and reproducing apparatuscan produce a good reproduced picture in a wide tape speed range from alow speed to a high speed.

Second Embodiment

A second embodiment of the present invention will be explained.

FIG. 40 is a block diagram of a DTF control system in a secondembodiment of the present invention. This embodiment is different fromthe first embodiment in that an element which is the same as the tensionestimating device 132 used in the first embodiment for the detection ofa tension and constituted by an external disturbance observer in themodern control theory is provided in the tape drawing actuator 61 as atape drawing actuator external disturbance estimating device 170. Sincethe principle and the structure of the external disturbance estimatingdevice 170 are completely the same as those of the tension estimatingdevice 132 in the first embodiment, as shown in FIG. 41, an explanationthereof will be omitted.

The estimated external torque disturbance, which is the output of thetape drawing actuator external disturbance estimating device 170 and isapplied to the actuator driver 65 is positively fed back after it ismultiplied by R'_(T) /K'_(TZ), which is the inverted characteristic ofthe tape drawing actuator electrical characteristic K'_(TZ) /R'_(T) by acircuit 171 so as to cancel the external torque disturbance. Theexternal disturbance suppressing characteristic at that time is shown inFIG. 42.

When an external disturbance suppression loop is newly provided in thetape drawing actuator 61 in this way so as to cancel the externaldisturbance, the position of the tape drawing actuator 61 is fixed as ifthere were no external disturbance with respect to an externaldisturbance in the suppression controlled region of the externaldisturbance suppression loop (within about 1 KHz in the example shown inFIG. 42) which is caused by, for example, the vibration of a VTR deckmounted on an automobile. The tape drawing actuator 61 is moresusceptible to an external disturbance than the head actuator 76 becausethe mass of the movable portion of the tape drawing actuator 61 islarge, and the tape drawing actuator 61 is a cantilever arm system whichis not supported by a spring. This suppression loop is therefore veryeffective.

In a control system having the above-described structure, since the tapetension actuator 61 does not vibrate even due to a sudden externaldisturbance such as the vibration of the VTR deck, constant stable DTFcontrol is enabled.

As described above, according to this embodiment, a tracking errorcorrection device is newly provided as a movable roller in a tape travelpath outside of the drum. DTF control is carried out in a two-stagecoupling system in a wide frequency band and a wide dynamic range with ahigh accuracy. In addition, the tension is detected by an externaldisturbance observer so as to constitute a tension control systemcapable of tension control in a wide frequency band and a wide dynamicrange with a high accuracy. Accordingly, this embodiment enables goodreproduction not only in normal-speed reproduction but also inreproduction at a speed selected from a wide range.

Third Embodiment

In the above embodiments, the tape drawing actuator and the tape tensionactuator help the DTF control of the magnetic head and carry outhigh-speed noiseless reproduction. In the present embodiment, theoptimum tension control is enabled by using only the tape tensionactuator. A third embodiment which enables suitable tape tension controlonly by the tape tension actuator will be explained hereinunder.

The structure of the tape tension actuator in the third embodiment isthe same as those of the first and second embodiments. Tension controlis also carried out in a wide frequency band with a high accuracy by afeedback system which presumes the relationship between an input voltageand displacement in the same way as in the first and second embodiments.

Structure of Tape Tension Actuator

FIG. 43 shows a structure of a tape tension actuator similar to that ofthe tape tension actuators 62 in the first and second embodiments,respectively.

In FIG. 43, a tape 201 fed from a feed reel 200 is introduced to arotary drum 204 through fixed pass rollers 202 and 203.

A tape tension actuator 205 includes a rocking arm 206 and a tensionroller 207 provided at one end thereof is moved in the directionindicated by the arrow and adjusts the tension of the tape which comesinto contact therewith, as desired.

The rotary shaft of the rocking arm 206 is represented by the referencenumeral 208, and a permanent magnet 209 is fixed at the other end therocking arm 206. Around the permanent magnet 209, an exciting coil 209is fixed and, as a result, by supplying a predetermined exciting currentto the exciting coil 210, the permanent magnet 209 is moved to apredetermined position, as desired.

In FIG. 43, the exciting coil 210 is fixed on a yoke 211. The yoke 211has a magnetic shielding effect for preventing the leakage of a magneticflux to the outside. The rocking arm 206 is rockably supported by agimbal spring 212 or the like.

Although FIG. 43 schematically shows the structure of the tensionactuator 205, the concrete structure of thereof can be the same as thatshown in FIGS. 15 and 16.

FIG. 44 shows a modification of this embodiment. In this modification, atension arm 212 is directly connected to the permanent magnet 209, andthe tension arm 212 and the tension roller 207 linearly move, as shownin FIG. 44.

In this embodiment, the position of the tension roller 207 is constantlydetected and compared with the reference value or an estimated externaldisturbance value for a predetermined tension control. FIG. 45 shows aposition sensor of the tape tension actuator 205 shown in FIG. 43.

A position sensor 214 includes a light emitting device such as a laserdiode or an LED and a separation light receiving device 216 such as aphotodiode.

The rocking arm 206 is provided with a reflecting mirror 217 forreflecting the light from the light emitting device 215, and thereflected light enters the light receiving device 216 after it isconverted into parallel rays by a lens 218.

Therefore, the amount of light entering the light receiving device 216or the position at which light enters the light receiving device 216 ischanged by the rocking motion of the rocking arm 206, whereby theposition of the tension roller 207 is electrically detected.

FIG. 46 is another example of the position sensor 214. The positionsensor 214 includes a light emitting device 219, a collimator lens 220and a light receiving device 221, and each of these elements issupported in a fixed state by a holder 222.

The rocking arm 206 is provided with a light shielding portion 207a andthe interruption by the light shielding portion 207a between the lightemitting device 219 and the light receiving device 221 enableselectrical position detection.

Positional detection is also possible by a magnetic sensor. FIG. 47shows an example of such a magnetic sensor.

In FIG. 47, a permanent magnet 223 is fixed to the rocking arm 206, andtwo Hall elements 224 and 225 are fixed in the vicinity of the permanentmagnet 223. By comparing the outputs of both Hall elements 224, 225 by adifferential amplifier 226, it is possible to obtain a desired positionsignal.

Such a magnetic sensor is incorporated into the tape tension actuator205, as shown in FIG. 48.

The tape tension actuator 205 shown in FIG. 48 is the same as that shownin FIG. 44 and the permanent magnet is fixed to a part of the tensionroller 207 which is fixed to the tension arm 213.

Tension Control System

An example of a tension control system using the tape tension actuator205 and the position sensor 214 is shown in FIG. 49. This control systemresembles the control system in the first embodiment shown in FIG. 26.

This control system is characterized in that the external tensiondisturbance is electrically estimated by an external tension disturbanceestimating device 230 from the input voltage of the tape tensionactuator 205 and the displacement of the tension roller detected by theposition sensor 214.

This control system is further characterized in that the tension errorobtained by comparing the estimated value with the reference value isdivided into a high-frequency component and a low-frequency component,the former being supplied to the tape tension actuator 205 and thelatter to the feed reel motor 233.

The high-frequency component of the tension error is supplied from acompensator and a driver 231 to the tape tension actuator 205, and thelow-frequency component thereof is supplied from a compensator and adriver 232 to the feed reel motor 233.

When the tape tension actuator 205 and the feed reel motor 233 correctthe errors, these changes in tension are replaced by characteristiccircuits 234 and 235 and fed back to the tape tension actuator 205.

In FIG. 49, the tension change caused by the displacement of the tapetension actuator 205 and the tension change caused by the displacementof the feed reel motor 233 are first added. To the sum is then added anexternal disturbance such as an external disturbance produced by thefriction between the shaft and the drum which is received by the tapeand a change in the frictional coefficient of the tape, and the totalsum is fed back to the tape tension actuator 205. That is, this totalsum represents the total tension of the magnetic tape travelling system.In this way, with due consideration of all elements of a tension error,this control system enables tension correction in a wide frequency bandwith a high accuracy.

FIG. 50 is obtained by converting the block diagram of the tensioncontrol system shown in FIG. 49 into the transfer functions of thecontrol theory. The symbol s is a Laplace operator.

The reference numeral 236 represents a transfer function including thecoil resistance R in the tape tension actuator 205 and the forceconstant K_(tR) of the electromagnetic driver, and 237 represents atransfer function including the spring constant k of the tape tensionactuator 205 and mass M of the movable portion. The reference numeral238 represents a transfer function circuit electrically simulating thetransfer function 236, and the reference numeral 239 represents atransfer function which constitutes a feedback loop together withtransfer function circuits 240 and 241 and simulates the transferfunction 237 by the equivalent conversion of the control theory. Thereference numerals 242 and 243 are the feedback gains of the observer(tension control system) which are fed back so as to converge thedifferences between the output of the position sensor 214 and therespective outputs of the transfer function circuits 239 to 241 are onzero in order that the dynamic characteristics of the transfer functions238 to 241 which simulate the characteristic of the tape tensionactuator 205 agree with the characteristic of the actual tape tensionactuator 205.

The reference numeral 244 represents a high pass filter, which is a partof the compensator for feeding back a comparatively high frequencycomponent in the controlled region in the tension control system to thetape tension actuator 205, and 245 represents a low pass filter, whichis a part of the compensator for feeding back a comparativelylow-frequency component in the controlled region of the tension controlsystem to the feed reel motor 233. The reference numeral 246 representsthe gain of an amplifier for determining the loop gain of a feedbackloop with respect to the tape tension actuator 205 and the referencenumeral 247 represents the gain of an amplifier for determining the loopgain of the feedback loop with respect to the feed reel motor 233. Thereference numeral 248 represents a transfer function indicating the coilresistance R_(L) and the torque constant K_(tL), and 249 represents atransfer function indicating the rotational inertia J of the feed reelmotor 233.

Operation of Third Embodiment

The operation of the tension control system in the third embodiment willnow be explained.

In a conventional tension control, when the force of the spring 22 isbalanced with the tape tension, the amount of displacement of thetension control arm 21 is regarded as the tension, and the amount ofdisplacement is fed back to the reel motor 6 as the detected tensionvalue, as shown in FIG. 81.

Strictly speaking, however, it is up to the spring resonance frequencyof the tension control arm 21 which is supported by the spring that theamount of displacement of the tension control arm 21 supported by thespring is proportional to the tape tension, and beyond the springresonance frequency, the phase of the change in the tension applied tothe tension control arm 21 is deviated from the phase of the change inthe position of the tension control arm 21. Actually, the phase isshifted by 90 degrees at the spring resonance frequency and by 80degrees at a higher frequency. As a countermeasure, in a conventionaltension control system, the controlled region is limited by the phaseshift of the spring support system including the tension control arm 21.This means that the tension detectable by the tension control arm 21 islimited to the frequency band of not higher than the spring resonancefrequency of the spring support system including the tension control arm21. It will naturally be considered to lighten the tension control armor increase the spring constant in order to heighten the springresonance frequency. However, there is a limitation in lightening thetension control arm, and if the spring constant is increased, thetension control arm 21 does not move much even if there is a change intension, for thereby lowering the detection accuracy.

In contrast, in this embodiment, it is possible to detect tension in awide frequency band irrespective of the spring resonance frequency ofthe tension control arm 21.

In this embodiment, a tension estimating device constitutes what iscalled a co-dimensional observer (hereinunder referred to as "tensionestimating device") in the modern control theory which electricallysimulates the transfer characteristic (driving current or inputvoltage/displacement) of the tape tension actuator. It is thereforepossible to detect the tape tension applied to the tape tension actuatorin a wider frequency band in comparison with the conventional mechanicaltension detector such as that shown in FIG. 81.

The above-described principle will be explained in more detail. FIG. 50shows the transfer functions of the tension estimating device.

In FIG. 50, when a driving voltage to be input to the tape tensionactuator 205 is input to the circuit which simulates the coil resistanceR and the force constant K_(t), the output b' of the tension estimatingdevice 230 becomes the estimated value of the actual driving force b ofthe tension control system. If the transfer functions of the circuits239, 240 and 241 which constitute the feedback group are equivalentlyconverted by the control theory, the following equation holds: ##EQU10##That is, the transfer function circuits 239, 240 and 241 simulate thetransfer function circuit 237 of the tape tension actuator 205.Therefore, when the output b' of the transfer function circuit 238 isinput, the output d' of transferring the transfer function circuits 239,240 and 241 ought to be the estimated value of the output d of the tapetension actuator 205. However, the transfer function circuits 239, 240and 241 are provided with an integrator therewithin, and even if thetransfer functions are the same as the characteristic output from thetransfer function circuit 237 in the tape tension actuator 205 withrespect to the frequency characteristics, the dynamic characteristicsthereof are not equal thereto due to a difference in the initial valuesof the integrators. Therefore, the difference e between the actualamount of displacement d" detected by the position sensor 214 and theestimated value d' of the tension estimating device 230 is fed back atgains of f₁ and f₂, whereby the dynamic characteristics as well as thefrequency characteristics agree with those of the actual tape tensionactuator 205.

The above-described structure is well known as the structure of aco-dimensional observer in the modern control theory. It is in order tofreely determine the convergence of the observer that the signals arefed back in the two loops at the gains of F₁ and F₂ to the inputterminals of the transfer function circuits 239 and 240 which includethe integrator (1/S in a Laplace conversion) in the model of the tapetension actuator 205. A co-dimensional observer to which the drivingvoltage and the displacement of an object of control are input isgenerally used to estimate the internal speed thereof. If the feedbackgains f₁, f₂ of the co-dimensional observer are adequately larger thanthe pole of the observer (the negative real number is large), in otherwords, if the values of f₁, f₂ are large (high gains), in the state inwhich the dynamic characteristic and the static characteristic of theobject of control agree with each other, it is possible to estimate thetension. At this time, since the dynamic characteristic agrees with thestatic characteristic, the following relationship holds:

    d'≈d                                               (21)

The relationship between the poles is the same as in FIG. 30 for thefirst embodiment.

Since the transfer function circuit 236 and the model thereof do notinclude an integrator, the driving force b' is represented as follows:

    b'≈b                                               (22)

Since the dynamic characteristic of the object of control agrees withthat of the model in the observer, the speed and the acceleration aswell as the displacement agrees those of the model. Therefore, the forcec' applied to the arm of the tape tension actuator 205, which isequivalent to M times of the acceleration is represented as follows:

    c'≈c                                               (23)

Since the sum of the driving force b and the torque a is the torque c inthe original tape tension actuator 205, as in the following equation;

    b+a=c                                                      (24)

the following relationship holds from the formulas 21 to 24:

    b'+a=c'

    b'-c'=a                                                    (25)

that is,

    a'=a                                                       (26)

This means that a' in the signal path in the observer represents atension, and that it is possible to detect the tension irrespective ofthe spring resonance of the tension mechanism by taking out a'.

The estimated tension a' is compared with the reference tension value,and only the high-frequency component of the tension error is taken outby the high pass filter 244 and fed back to the tape tension actuator205 at a gain of f₃. Simultaneously, the low-frequency component istaken out by the low pass filter 245 and fed back to the feed reel motor233 at a gain of f₄. The reason why the frequency band is divided asdescribed above is because the tape tension actuator 205, which has asmall mechanical time constant, is generally suitable for the control ina high-frequency band but since the movable range is limited, it isimpossible to control a change in the tension which has a controlledvaluable approximate to that for a direct current.

In the pole-positioning of the feedback gains f₃ and f₄, for example,the points which are closer to the original point than to the pole ofthe observer (for example, about 1/10 of the pole 157 by the realnumber) are selected for the pole of the tension control loop to thetape tension actuator 205 and the pole of the loop to the feed reelmotor 55. This relationship is also the same as in FIG. 30 for the firstembodiment.

FIG. 34 shows the transient behavior of the estimated externaldisturbance at this time. The actual tension value agrees with theestimated tension value after a constant time.

In the above system, the principle and the operation of the tensioncontrol in the third embodiment have been explained. In some cases, thepermanent magnet 209, the exciting coil 210, the yoke 211, etc. shown inFIG. 43 cannot be mounted on the actual tape tension actuator 205 due tothe limitation in space or cost.

According to the tension control system in this embodiment, even in thecase in which the tension roller cannot be controlled by anelectromagnetic driving device, as described above, it is possible tocontrol a tension in a wider frequency band than a conventional tensioncontrol system. An example is shown in FIG. 51. FIG. 51 is obtained byreplacing the input voltage of the tape tension actuator 205 constant of0, and the input voltage of the external tension disturbance estimatingdevice 230 by a constant 0.

The operation of the tension control system shown in FIG. 51 is the sameas the operation of the tension control system shown in FIG. 50 exceptthat in the formulas 20 to 26, it is assumed that b=0, b"=0. In thiscase, the a' in the signal path in the external tension disturbanceestimating device 230 is the estimated external tension disturbance.Therefore, after a' is compared with the reference tension, it is fedback to the feed reel motor 233 at a gain of f₄, for thereby enabling achange in the tension of the magnetic tape travelling system to besuppressed in a wider frequency band than a conventional tensionmechanism.

When the tension is controlled by the above-described method ofestimating the external tension disturbance, the estimated tension isexactly detected up to a much higher frequency than that substituted bythe amount of displacement of the tension control arm as in aconventional tension control mechanism, for thereby realizing tensioncontrol in a very wide frequency band.

The open loop characteristic such as that shown in FIG. 25 can also beobtained in the tension control system shown in FIG. 50. That is, if thegain of the loop of the tape tension actuator 205 in a high-frequencyrange is made higher than that of the loop of the reel motor, forexample, 20 dB/ded, so as to suppress the phase shift to not more than90° in the controlled region and to secure the stability as a whole, itis possible to secure the gain of the reel motor loop in a low-frequencyrange.

Since loops are complicatedly intertwined in such tension control unlikein a simple feedback loop having one input and one output, a largeamount of operation is required. Although the integrator, amplifier,adder, subtracter or the like can naturally be constituted by an analogcircuit by using an operational amplifier or the like which produces fewoffsets and drifts, since such an amplifier is expensive and the circuitgrows to a large scale, it is desirable to digitally operate by amicrocomputer or the like. The structure of the hardware in the controlsystem shown in FIG. 50 which is constituted by a microcomputer is suchas that shown in FIG. 36 for the first embodiment. It is possible torealize the control system having very little hardware, as shown in FIG.36.

As described above, according to this embodiment, since the tape tensionactuator 205 suppresses a tension change in the high-frequency band andthe feed reel motor 233 suppresses a tension change in the low-frequencyband, the tension control accuracy is enhanced and a tension controlsystem capable of tension control with a high accuracy in a widefrequency band and a wide dynamic range is realized.

Additionally, the actuator in this embodiment has a performance equal tothe performance of a ceramic actuator of a piezoelectric element or thelike, a rotary motor, an ultrasonic motor or the like.

As described above, according to this embodiment, the tension which thetension roller receives from the magnetic tape travelling system isestimated by the tension control system and a driving signal based onthe output signal of the position sensor is fed back to either or boththe tape tension actuator and the reel motor so that the estimatedtension agrees with the reference tension. Consequently, it is possibleto enlarge the tension controlled region, increase the amount ofsuppression of tension change and enhance the control accuracy. Thus,the present embodiment is especially effective for the tension controlof a digital VTR or a high-definition VTR and the magnetic head of whichis required to have a high recording density and which is required tocontrol the space between the magnetic head and the magnetic tape to aconstant value.

Structure of Tape Actuator

The concrete structure of the tape drawing actuator and the tape tensionactuator which are used in each of the above-described embodiments willbe described hereinunder.

FIGS. 52 to 56 show the concrete structure of a tape actuatorincorporating a position sensor. A yoke holder 251 is fixed to a VTRbase 250, and a yoke 252 is integrally fixed on the holder 251. Asupporting shaft 253 is implanted in the yoke holder 251 and a rollerarm 257 is rotatably supported by a support shaft 253 through upper andlower bearings 255, 256. A tape pass roller 258 is rotatably supportedat the free end of the roller arm 257, so that when a magnetic tape (notshown) comes into contact with the roller 258, a predeterminedstretch/relaxation or a desired tension value is imparted to themagnetic tape, as described above. The roller shaft 259 of the tape passroller 258 is firmly fixed to the roller arm 257 by a screw 260, andadjustment of the tape pass roller 258 in the direction of the height iscarried out by a screw 258a provided on the roller shaft 259.

A driving coil 262 is fixed to a coil holder 261 which is provided atthe other end of the roller arm 257. The driving coil 262 can displacethe tape pass roller 258 around the support shaft 253 by a given anglein cooperation with a permanent magnet 263 which is fixed to the yokeholder 251, as described above.

In order to detect the position of the displacement of the roller arm257, a light emitting device 264 such as a laser diode is provided onthe roller arm 257, and the light which has passed through a slit plate265 is emitted in the direction indicated by the arrow in FIG. 52.

The radiated light 266 is received by a one-dimensional type lightreceiving device 267 which is fixed on the yoke 252, whereby theposition of the displacement of the roller arm 257 is electricallydetected.

As is clear from FIG. 54, the permanent magnet 263 has a configurationof a sector and is divided into two parts in the direction of therotation of the driving coil 262.

FIG. 55 shows the light emitting device 264 and the slit plate 265. Thelaser beams radiated from a light emitting element 268 such as a laserdiode are converted into parallel rays by a collimator lens 269. Theparallel rays are emitted through the slit 265a of the slit plate 265 asslit light 266 having an oblong section.

FIG. 56 shows the slit light 266 radiated onto the light receivingsurface 267a of the one-dimensional type light receiving device 267. Asis clear from FIG. 56, it is possible to detect the position of the tapepass roller 258 from the slit light 266 which moves to the right-hand orleft-hand direction.

As the light emitting device, an LED may be used in place of the laserdiode.

FIG. 57 shows another example of an actuator which resembles that shownin FIG. 52. The same numerals are provided for the elements in FIG. 57which are the same as those shown in FIG. 52, and an explanation thereofwill be omitted.

In the example shown in FIG. 57, a magnetic element, but not an opticalelement, is used as the position sensor.

A Hall element, 270 is fixed on the distal end 257a of the roller arm257, and a magnet 271 is fixed on the base 251 at the position facingthe Hall element 270. The relative relationship between the Hall element270 and the magnet 271 displaces with the rotation of the roller arm257, whereby the position of the tape pass roller 258 is electricallydetected.

FIG. 58 shows still another example of an actuator. In this actuator,the position sensor is composed of a reflecting mirror 272 fixed on therotary shaft of the arm 258. The laser beams radiated from a lightemitting device 273 is reflected by the mirror 272 and received by alight receiving device 274, whereby the rotational angle of the rollerarm 257 is electrically detected.

FIG. 59 shows another example of the permanent magnet 263 shown in FIG.54. As is obvious from FIG. 59, the permanent magnet 263 is composed oftwo connected trapezoidal magnets.

FIG. 60 shows a further example of the actuator shown in FIG. 52. Alight shielding plate 275 is provided between the slit plate 265 and thelight receiving device 267 so as to prevent the ingress of the outsidelight.

FIGS. 61 and 62 show examples of the position sensor composed of acombination of a Hall element 276 and a magnet 277. In FIG. 61, the Hallelement 276 is fixed on the roller arm 257. In FIG. 62, the Hall element276 is provided at the protruding portion 257b at the distal end of theroller arm 257.

Structure of VTR Incorporating Tape Actuators

As described above, in the present embodiment, the tape actuators aredisposed at least on one side of the entrance side and the exit side ofthe rotary drum so as to enable DTF control, high-speed noiselessreproduction or tape tension control.

Embodiments of the present invention in which the above-described tapeactuators are incorporated into a digital VTR or the like will beexplained hereinunder.

FIG. 63 schematically shows the structure of a digital VTR in which atape tension actuator and a tape drawing actuator are provided on theentrance side and on the exit side, respectively, of a rotary drum.

A tape cassette 301 is mounted on the base 300 of a VTR deck, and thetape 302 is loaded on a rotary drum 304 accommodating magnetic heads303a and 303b.

In order to drive a feed reel 305 and a take-up roll 306 of the cassette301, a feed reel motor 307 and a take-up reel motor 308 are provided inthe cassette deck.

FIG. 63 shows the state in which the tape is loaded. The tape 302 fedfrom the feed reel 305 is introduced to the rotary drum 304 throughguides 309, 310, a fixed tape pass roller 311 to be described later, atension roller 312, a fixed tape pass roller 313 and a slant pin 314.

On the exit side of the rotary drum 304, the tape 302 is introduced to acapstan 319 through a slant pin 315, a fixed tape pass roller 316, tapedrawing roller 317 and a fixed tape pass roller 318. A pinch roller 320is pressed against the capstan 319, and the tape 302 is furtherintroduced to the take-up reel 306 through guides 321 and 322.

A tape tension actuator is represented by the reference numeral 323, anda tension roller 302 is supported at the end of a tension arm 325 whichis rockably supported by a support shaft 324 of the tape tensionactuator 323, as described above. A signal from the position sensor 262which is accommodated in the tape tension actuator 323 is supplied tothe tension controller, as described above, and a control signal issupplied from the reel motor controller 327 to the feed reel motor 307.

A tape drawing actuator 328 has a rocking arm 330 supported by a supportshaft 329, and the tape pass roller 317 is fixed at the end of the arm330. A signal obtained from a position detecting device 331 which isaccommodated in the tape drawing actuator 328 is supplied to an actuatorcontroller and a capstan controller. This signal is also supplied to areel motor controller 332 and controls the take-up reel motor 308.

FIG. 63 shows the digital VTR in the state of normal-speedrecording/reproduction, and FIGS. 64 and 65 show the digital VTR in thestate of superior reproduction in which the actuators are differentiallyoperated. The operations of the digital VTR in the respective stateswill be explained in the following discussion.

At the time of normal-speed recording/reproduction, a tape travel pathsimilar to a conventional one is formed, as shown in FIG. 63, and themagnetic tape 302 is fed from the feed reel 305 to the take-up reel 306at a constant speed by the capstan 319.

The movable tape pass roller 317 of the tape tension actuator 328 on thetake-up side is mechanically or electrically fixed at a predeterminedposition. On the other hand, the tension roller 312 of the tape tensionactuator 323 is pressed against the magnetic tape 302 at a constantforce. Simultaneously, the feed reel motor 307 is so controlled that thetension of the magnetic tape 302 takes a desired value. As a result, thebalance of the tension roller 312 is kept at the position at which thetension of the magnetic tape 302 takes a desired value. This position isdetected by a position detecting device 326 as the reference position ofthe tension roller 312. By radiating the oblong or elliptic light fromthe light emitting portion in the method shown in FIG. 55, it ispossible to enhance the detection sensitivity and make the relativepositional relationship between the ray 266 and the light receivingdevice 267 loose in the direction orthogonal to the direction of therotation of the tension roller 312. When the diameter of the magnetictape 302 wound around the feed reel 305 changes with the travel of themagnetic tape 302, the tension changes, and with this change, theposition of the tension roller 312 deviates from the reference position.The position detecting device 326 detects the amount of movement of thetension roller 312 and controls the feed reel motor 307 so as to restorethe tension roller 312 to the reference position.

If the tension is changed by an external disturbance, the balance offorces is lost and the tension roller 312 moves from the referenceposition. This amount of movement is also detected by the positiondetecting device 326, and the feed reel motor 307 is controlled so thatthe tension roller 312 is restored to the reference position.

At the time of fast-forward at which the magnetic tape 302 is fed fromthe feed reel 305 to the take-up reel 306 at a high speed, control ofthe tension is carried out in the same way. At this time, the tensionvalue may be set at a different value from that for normal-speedrecording/reproduction.

At the time of rewinding at which the magnetic tape 302 is fed from thetake-up reel 306 to the feed reel 305 at a high speed, control of thetension is carried out the other way around. That is, the tension roller312 is fixed at a predetermined position, and in accordance with theamount of deviation of the movable tape pass roller 317 from thepredetermined position detected by the position detecting device 331,the take-up reel motor 308 is so controlled as to keep the tensionconstant.

The case in which superior reproduction is carried out at a speeddifferent from the speed at which the signals are recorded will now beexplained.

In superior reproduction, a method of tracing the recording track on themagnetic tape 302 by moving the magnetic head 303 itself in thedirection of the width of the track and a method of tracing therecording track by moving both the magnetic head 303 itself and themovable rollers 312, 317 are adopted, and these two methods are switchedover each other depending upon the tape feeding speed.

In the case of moving only the magnetic head 303, the tension iscontrolled in the same way as at the time of fast-forward when themagnetic tape 302 is fed from the feed reel 305 to the take-up roll 306,while the tension is controlled in the same way as at the time ofrewinding when the magnetic tape 302 is fed from the take-up reel 306 tothe feed reel 305.

In the case of moving both the magnetic head 303 and the movable rollers312, 317, the tension roller 312 and the movable tape pass roller 317are moved by the same distance in the reverse phases in linkage witheach other.

The structure of a VTR deck incorporating tape actuators in accordancewith the present embodiment will be understood from the aboveexplanation.

In the present embodiment, since the movable pass roller and the tensionroller move with respect to the fixed tape pass rollers, it is necessaryto exactly regulate the position of the tape both in the direction ofthe travel and in the direction of the height so as to feed the tape tothe cylinder groove of the rotary drum. In addition, a simple and highlyaccurate structure for drawing the magnetic tape from the tape cassetteand loading it on the rotary drum for the purpose of recording orreproducing is required.

To meet such demand, the present embodiment also provides a magneticrecording and reproducing apparatus including a new tape loadingmechanism. A preferred embodiment thereof will be shown in FIGS. 66 to69.

The main parts of FIGS. 66 and 67 are the same as FIG. 63. The samenumerals are provided for the elements which are the same as those inFIG. 63, and an explanation thereof will be omitted.

FIG. 66 shows the recording/reproducing state after loading the tape,and FIG. 67 shows the state before loading the tape in which thecassette is inserted.

The guide 310 on the entrance side and the guide 321 on the exit sideare movable before and after tape loading as in the known systems, andthe details thereof will be omitted.

The fixed tape pass rollers 311, 313 and the slant pin 314 must be movedbefore and after tape loading in order to draw the magnetic tape 302from the cassette and introduce it to the entrance side of the rotarydrum 304. The present embodiment is characterized in that both the fixedtape pass rollers 311, 313 and the slant pin 314 are fixed on one tapeloader 340 and integrally moved, for thereby enabling the exactpositioning of each tape guide.

Similarly, on the exit side of the rotary drum 304, the slant pin 315and the fixed tape pass rollers 316, 318 are fixed on one tape loader341 on the exit side, for thereby enabling integral tape loading and theexact positioning of the magnetic tape 302 on the exit side.

Although the details are omitted in FIG. 67, the tape loader 340 on theentrance side and the tape loader 342 on the exit side are introduced toguide grooves 342 and 343, respectively, which are provided on the deckbase 300. The tape loaders 340, 341 are vertically and movably providedin order to introduce the magnetic tape 302 to the rotary drum 304 andcatch the magnetic tape 302 of the tape cassette 301.

The deck base 300 is also provided with a catch 344 on the entrance sideand a catch 345 on the exit side which can exactly position the fixedtape pass rollers 313 and 316 after tape loading, as shown in FIG. 63.

FIG. 68 shows the travel path of the magnetic tape 302 after tapeloading.

As is obvious from FIG. 68, on the entrance side of the rotary drum 304,the fixed tape pass rollers 311, 313 and the slant pin 315 arepositioned only by the tape loader 340 on the entrance side in order toexactly position the magnetic tape 302 with respect to the tensionroller 312 of the tape tension actuator.

Similarly, on the exit side of the rotary drum 304, the tape loader 341on the exit side exactly positions the slant pin 315 and the fixed tapepass rollers 316 and 318.

The present embodiment is further characterized in that the pair offixed tape pass rollers regulate the position of the upper and lowerends of the magnetic tape 302 on the entrance side and exit side byflanges in order to regulate the position in the direction of the widthof the magnetic tape 302. In this way, the magnetic tape 302 is exactlyfed to a predetermined cylinder groove of the rotary drum 304, forthereby reducing the generation of a tracking error. The upper flange316a of the fixed tape pass roller 316 regulates the upper end of themagnetic tape 302, and the lower flange 318a of the fixed tape passroller 318 regulates the lower end of the magnetic tape 302.

In this way, the magnetic tape 302 can pass the travel path in the stateof being exactly positioned in the vertical direction.

FIG. 69 is an enlarged view of the tape loader 341 on the exit side.

In order to exactly position the flanges of the fixed tape pass rollers316, 318, height adjusting screws 316b and 318b are provided at thefixed portion of the fixed tape pass rollers 316 and 318, respectively,for thereby adjusting the heights of the respective tape pass rollers atthe time of assembly.

The fixed tape pass rollers 311, 313 provided on the tape loader on theentrance side of the rotary drum 304 also regulate the upper and lowerends of the magnetic tape 302. As shown in FIG. 68, the lower flange311a of the fixed tape pass roller 311 regulates the lower end of themagnetic tape 302 and the upper flange 313a of the fixed tape passroller 313 regulates the upper end of the magnetic tape 302. Theadjustment of the height of each roller on the tape loader 340 iscarried out in the same way as on the exit side.

As described above, the tape actuators in accordance with the presentembodiment are mounted on a digital VTR deck.

In the above-described embodiment, however, since the actuators and thetape loaders are mounted on the upper side of the deck base, it issometimes difficult to arrange these elements in a narrow space.

Accordingly, it is preferable to arrange either of the actuators andloaders on the upper surface and the other on the under surface in orderto enhance the space utility.

FIGS. 70 to 74 show a preferred embodiment of the present invention inwhich either of these elements is disposed on the upper surface and theother on the under surface of a VTR deck.

In FIGS. 70 to 74, the same numerals are provided for the elements whichare the same as those in FIG. 63, and an explanation thereof will beomitted.

FIG. 70 shows a recording/reproducing state after the completion of tapeloading and FIG. 71 shows the state before tape loading in which thetape cassette 302 is inserted into the deck.

The structure of the tape actuators in this embodiment will first beexplained.

FIG. 72 shows an example of a tape tension actuator 350. Since a tapedrawing actuator 351 has the same structure, a detailed explanationthereof will be omitted.

In FIG. 72, a support shaft 352 is fixed on the deck base 300 and atension arm 355 is rotatably supported by the support shaft 352 throughbearings 353, 354. At the end of the tension arm 355, a tension roller356 is provided. This embodiment is characterized in that the tensionarm 355 is disposed on the under surface of the base 300. The tensionroller 356 projects into the upper side of the base 300 from theunderside of the base 300 through a guide groove 357 provided on thebase 300.

According to this embodiment, no part of the driving portion of the tapeactuator is disposed on the upper surface of the base 300, for therebyfacilitating the mounting of other elements such as a tape loader on theupper surface of the base 300.

As is clear from FIG. 72, a driving coil 358 is provided on the tensionarm 355 in such a manner as to integrally rotate therewith. On the undersurface of the base 300, a holder yoke 359 is fixed. A permanent magnet360 is fixed on the holder yoke 359 and a yoke 360 is provided on theholder yoke 359.

As is clear from the first embodiment, by supplying a predeterminedcurrent to the driving coil 358, it is possible to position the tensionroller 356 at any given position by the electromagnetic action with thepermanent magnet 360.

In FIG. 72, the guide groove 357 is provided with a roller insertionhole 357a which has a larger diameter than the other groove portion, forthereby enabling the tension roller 356 of a large diameter to be easilyinstalled from the under surface of the base 300 toward the uppersurface thereof.

In this embodiment, the guide groove 357 not only forms the path alongwhich the tension roller 356 moves but also the guide groove throughwhich the support shaft of the tape loader passes. By continuouslyproviding the tension roller path and the guide groove in this way,machining is facilitated.

The tape drawing actuator 351 has the same structure. In FIG. 71, themovable tape pass roller 362 is shown. The groove for allowing thepassage of the movable tape pass roller 362 is a guide grooverepresented by the reference numeral 363 and the roller insertion holehaving a large diameter is represented by the reference numeral 363a.

The guide groove 363 on the exit side is also used as the groove throughwhich the support shaft of a later-described tape loader passes.

As described above, according to this embodiment, the tape actuators350, 351 are disposed on the under surface of the deck base 300.

On the other hand, the tape loaders are disposed on the upper surface ofthe deck base 300. In FIG. 71, the tape loader on the entrance side isrepresented by the reference numeral 364 and the tape loader on the exitside is represented by the reference numeral 365.

On the tape loader 364, the fixed tape pass rollers 311, 313 and theslant pin 314 are integrally fixed. Similarly, the slant pin 315 and thefixed tape pass rollers 316, 318 are integrally fixed on the tape loader365 on the exit side.

The support shaft 366 of the tape loader 364 on the entrance side movesalong the guide groove 357 so as to safely introduce the magnetic tape302 to the rotary drum 304, as shown in FIGS. 70 and 71. Similarly, thesupport shaft 367 of the tape loader 365 on the exit side moves alongthe guide groove 363 so as to safely introduce the magnetic tape 302from the rotary drum 304.

As is clear from FIG. 70, the tape loader 364 on the entrance side isprovided with a relief groove 364a to which the tension roller 356 canmove. This relief groove 364a forms a space in which the tension roller356 moves at the time of high-speed noiseless reproduction, as shown inFIGS. 73 and 74.

Similarly, the tape loader 365 on the exit side is provided with arelief groove 365a to which the movable tape pass roller 362 can move.

As described above, according to this embodiment, the tension roller 356and the movable tape pass roller 362 differentially move and the tapeloaders 364 and 365 do not obstruct the movement of these rollers.

While there has been described what is at present considered to bepreferred embodiments of the invention, it will be understood thatvarious modifications may be made thereto, and it is intended that theappended claims cover all such modifications as fall within the truespirit and scope of the invention.

What is claimed is:
 1. A magnetic reproducing apparatus which is capableof controlling tension of a magnetic tape, the apparatus comprising:tapefeeding means for feeding said magnetic tape at a predetermined speed toa rotary drum accommodating a magnetic head; a tape tension actuator,provided on an entrance side of said rotary drum and including a movabletension roller which movably comes into contact with said magnetic tape,for changing a tension of said magnetic tape in accordance with an inputdrive voltage applied thereto; tension roller position detecting meansfor detecting a position of said movable tension roller and outputting adetected displacement signal indicative of the detected position; and atension control circuit for controlling the tension of said magnetictape on said movable tension roller, said tension control circuitincludinga simulation circuit for electrically simulating an (inputvoltage)/(displacement) dynamic transfer characteristic of arelationship between input drive voltage of said tape tension actuatorand displacement of said movable tension roller, said simulation circuitoutputting an estimated displacement signal indicative of an estimateddisplacement of said movable tension roller for the input drive voltageapplied to said tape tension actuator, a feedback circuit for obtainingan estimated error signal based on a difference between the estimateddisplacement signal and the detected displacement signal the estimatederror signal being fed back to said simulation circuit so that thedifference between the estimated displacement signal and the detecteddisplacement signal becomes zero, and conversion means, coupled to saidfeedback circuit, for converting the estimated error signal into atension estimation signal which represents an estimated tension of saidmagnetic tape on said movable tension roller, said tension controlcircuit outputting a tension control signal to said tape tensionactuator for controlling tape tension based on the tension estimationsignal, the tension control signal representing an amount of change intension of said magnetic tape on said movable tension roller caused byan external tension disturbance of said magnetic tape.
 2. The magneticreproducing apparatus according to claim 1, wherein said tape feedingmeans comprises:a feed reel on which said magnetic tape is wound; and afeed reel motor for driving said feed reel, said tension control circuitoutputting the tension control signal as divided according to frequencyband, a high-frequency component of the tension control signal beingnegatively fed back to said tape tension actuator and a low-frequencycomponent of the tension control signal being negatively fed back tosaid feed reel motor.
 3. A magnetic recording and reproducing apparatuswhich is capable of controlling tension of a magnetic tape to apredetermined value, the magnetic recording and reproducing apparatuscomprising:a rotary drum accommodating a magnetic head; a feed reelmotor for feeding said magnetic tape from a cassette at a predeterminedspeed; a pair of fixed tape pass rollers on an entrance side of saidrotary drum for introducing said magnetic tape supplied by said feedreel motor to a first predetermined position on the entrance side ofsaid rotary drum; a pair of fixed tape pass rollers on an exit side ofsaid rotary drum for drawing said magnetic tape from said rotary drum toa second predetermined position; a take-up reel motor for taking up saidmagnetic tape drawn from said fixed tape pass rollers on a take-up reelon the exit side at the predetermined speed; a tape tension actuator forapplying a tension to said magnetic tape in accordance with an appliedinput drive voltage, said tape tension actuator having a movable tensionroller which applies a tension to said magnetic tape by stretching saidmagnetic tape when said tape tension actuator displaces said movabletension roller between said fixed tape pass rollers on the entranceside; a tension roller position sensor for detecting the displacement ofsaid movable tension roller of said tape tension actuator and outputtinga detected displacement signal indicative of the detected displacement;a tension control means for controlling the tension of said magnetictape on said movable tension roller, said tension control meansincludinga simulation circuit for electrically simulating an (inputvoltage)/(displacement) dynamic transfer characteristic of arelationship between input drive voltage of said tape tension actuatorand displacement of said movable tension roller, said simulation circuitoutputting an estimated displacement signal indicative of an estimateddisplacement of said movable tension roller for the input drive voltageapplied to said tape tension actuator, a feedback circuit for obtainingan estimated error signal based on a difference between the estimateddisplacement signal and the detected displacement signal, the estimatederror signal being fed back to said simulation circuit so that thedifference between the estimated displacement signal and the detecteddisplacement signal becomes zero, and conversion means, coupled to saidfeedback circuit, for converting the estimated error signal into atension estimation signal representing an estimated tension of saidmagnetic tape on said movable tension roller, said tension control meansoutputting a tension control signal based on the tension estimationsignal, said tension control signal representing an amount of change intension of said magnetic tape on said movable tension roller caused byan external tension disturbance of said magnetic tape; and positioncontrol means for controlling the position of said movable tensionroller via said tape tension actuator on the basis of the detecteddisplacement signal and said tension control signal.
 4. The magneticrecording and reproducing apparatus according to claim 3, wherein saidtape tension actuator comprises a tension arm with said movable tensionroller fixed at one end thereof, an exciting coil being mounted on saidtension arm and a permanent magnet being fixed on an actuator base, saidmovable tension roller being displaced upon application of the drivevoltage across said exciting coil.
 5. The magnetic recording andreproducing apparatus according to claim 3, wherein said tension controlmeans supplies a high-frequency component of said tension control signalto said position control means and a low-frequency component of saidtension control signal to said feed reel motor.
 6. The magneticrecording and reproducing apparatus according to claim 3, wherein saidtape tension actuator comprises a tension arm with said movable tensionroller fixed at one end thereof, a permanent magnet being mounted onsaid tension arm and an exciting coil being fixed on an actuator base,said movable tension roller being displaced upon application of a drivevoltage across said exciting coil.
 7. A method for controlling tensionof a magnetic tape in a magnetic reproducing apparatus, comprising thesteps of:(a) feeding said magnetic tape at a predetermined speed to arotary drum accommodating a magnetic head; (b) driving a movable tensionroller of a tape tension actuator to be in contact with said magnetictape in accordance with an input drive voltage, said tape tensionactuator being provided on an entrance side of said rotary drum; (c)detecting a position of said movable tension roller; (d) electricallysimulating an (input voltage)/(displacement) transfer characteristic ofa relationship between input voltage of said tape tension actuator and adisplacement of said movable tension roller to provide an estimateddisplacement of said movable tension roller for the input drive voltageapplied to said tape tension actuator; (e) determining an estimatedtension of said magnetic tape on said movable tension roller based onthe estimated displacement of said step (d) and the detected position ofsaid step (c); and (f) controlling the tension of said magnetic tape onsaid movable tension roller, in accordance with the estimated tension ofsaid step (e), to be a reference tension.
 8. The method according toclaim 7, wherein said step (f) comprises:(f1) determining a differencebetween the estimated tension and the reference tension; (f2) providinga tension control signal in accordance with the determined difference ofsaid step (f1); and (f3) driving said movable tension roller with saidtape tension actuator in accordance with the tension control signal tocontrol the tension of said magnetic tape on said movable tensionroller.
 9. The method of claim 8, wherein said step (a) comprisesfeeding said magnetic tape from a feed reel using a feed reel motor. 10.The method according to claim 9, wherein said step (f2)comprises:dividing the tension control signal according to frequencyband; feeding back a high frequency component of the tension controlsignal to said tape tension actuator; and feeding back a low frequencycomponent of the tension control signal to said feed reel motor.
 11. Amethod for controlling tension of a magnetic tape in a magneticreproducing apparatus, comprising the steps of:(a) feeding the magnetictape from a cassette at a predetermined speed with a feed reel motor;(b) introducing the magnetic tape fed during said step (a) to a firstpredetermined position on an entrance side of a rotary drumaccommodating a magnetic head with a pair of fixed tape pass rollers onthe entrance side of said rotary drum; (c) drawing the magnetic tapefrom said rotary drum to a second predetermined position with a pair offixed tape pass rollers on an exit side of said rotary drum; (d) takingup the magnetic tape drawn from said fixed tape pass rollers on the exitside in said step (c) at the predetermined speed; (e) applying apredetermined tension to the magnetic tape by displacing a movabletension roller between said fixed tape pass rollers on the entrance sideto stretch the magnetic tape, said movable tension roller being drivenby a tape tension actuator in accordance with an input drive voltage;(f) detecting a displacement of said movable tension roller andproviding a detected displacement signal indicative of the detecteddisplacement; (g) determining an estimated tension of the magnetic tapeon said movable tension roller based on the detected displacement andthe input drive voltage; (h) estimating an external tension disturbanceand generating a tension control signal in accordance with apredetermined target tension of the magnetic tape on said movabletension roller and the estimated tension; and (i) driving said tapetension actuator with the detected displacement signal and said tensioncontrol signal to displace said movable tension roller so that thetension of the magnetic tape on said movable tension roller becomes thepredetermined target tension.
 12. The method according to claim 11,wherein said step (g) electrically simulates the relationship between andrive voltage of said tape tension actuator and an amount ofdisplacement thereof by an (input voltage)/(displacement) transfercharacteristic circuit.
 13. The method according to claim 11, whereinsaid step (i) comprises supplying a high-frequency component of saidtension control signal to said tape tension actuator and a low frequencycomponent of said tension control signal to said feed reel motor.
 14. Amagnetic reproducing apparatus which is capable of controlling tensionof a magnetic tape, the apparatus comprising:tape feeding means forfeeding said magnetic tape at a predetermined speed to a rotary drumaccommodating a magnetic head; a tape tension actuator provided on anentrance side of said rotary drum and including a movable tension rollerwhich movably comes into contact with said magnetic tape, said tapetension actuator driving said movable tension roller in accordance withan input drive voltage applied thereto; tension roller positiondetecting means for detecting a position of said movable tension rollerand outputting a detected displacement signal indicative of the detecteddisplacement; and tension control means for controlling the tension ofsaid magnetic tape on said movable tension roller said tension controlmeans includinga simulation circuit for electrically simulating an(input voltage)/(displacement) dynamic transfer characteristic of arelationship between input drive voltage of said tape tension actuatorand displacement of said movable tension roller, said simulation circuitoutputting an estimated displacement signal indicative of an estimateddisplacement of said movable tension roller for the input drive voltageapplied to said tape tension actuator, and conversion means, coupled tosaid simulation circuit, for converting the estimated displacementsignal into a tension estimation signal representing an estimatedtension of said magnetic tape on said movable tension roller, saidtension control means outputting the tension control signal asrepresentative of an amount of tension change caused by an externaltension disturbance on said magnetic tape based on the tensionestimation signal to drive said tape tension actuator to control tensionof said magnetic tape.
 15. A magnetic recording and reproducingapparatus which is capable of controlling the tension of a magnetic tapeto a predetermined value, the apparatus comprising:a rotary drumaccommodating a magnetic head; a feed reel motor for feeding saidmagnetic tape from a cassette at a predetermined speed; a pair of fixedtape pass rollers on an entrance side of said rotary drum forintroducing said magnetic tape supplied by said feed reel motor to afirst predetermined position on the entrance side of said rotary drum; apair of fixed tape pass rollers on an exit side of said rotary drum fordrawing said magnetic tape from said rotary drum to a secondpredetermined position; a take-up reel motor for taking up said magnetictape drawn from said fixed tape pass rollers on a take-up reel on theexit side at the predetermined speed; a tape tension actuator forapplying a tension to said magnetic tape in accordance with an appliedinput drive voltage, said tape tension actuator having a movable tensionroller which applies a tension to said magnetic tape by stretching saidmagnetic tape when said tape tension actuator displaces said movabletension roller between said fixed tape pass rollers on the entranceside; a tension roller position sensor for detecting the displacement ofsaid movable tension roller and outputting a detected displacementsignal indicative of the detected displacement; tension control meansfor controlling the tension of said magnetic tape on said movabletension roller, said tension control means includinga simulation circuitfor electrically simulating an (input voltage)/(displacement) dynamictransfer characteristic of a relationship between input drive voltage ofsaid tape tension actuator and displacement of said movable tensionroller, said simulation circuit outputting an estimated displacementsignal indicative of an estimated displacement of said movable tensionroller for the input drive voltage applied to said tape tensionactuator, and conversion means, coupled to said simulation circuit, forconverting the estimated displacement signal into a tension estimationsignal representing an estimated tension of said magnetic tape on saidmovable tension roller, said tension control means outputting a tensioncontrol signal as representative of an amount of tension change causedby an external tension disturbance on said magnetic tape based on thetension estimation signal; and position control means for controllingthe position of said movable tension roller via said tape tensionactuator on the basis of the detected displacement signal and saidtension control signal.